perf test: Fix libpfm4 support (63) test error for nested event groups

perf test: Fix libpfm4 support (63) test error for nested event groups

Compiling perf with make LIBPFM4=1 includes libpfm support and
enables test case 63 'Test libpfm4 support'. This test reports an error
on all platforms for subtest 63.2 'test groups of --pfm-events'.
The reported error message is 'nested event groups not supported'

 # ./perf test -F 63
 63: Test libpfm4 support                                            :
 63.1: test of individual --pfm-events                               :
 Error:
 failed to parse event stereolab : event not found
 Error:
 failed to parse event stereolab,instructions : event not found
 Error:
 failed to parse event instructions,stereolab : event not found
  Ok
 63.2: test groups of --pfm-events                                   :
 Error:
 nested event groups not supported    <------ Error message here
 Error:
 failed to parse event {stereolab} : event not found
 Error:
 failed to parse event {instructions,cycles},{instructions,stereolab} :\
	 event not found
 Ok
 #

This patch addresses the error message 'nested event groups not supported'.
The root cause is function parse_libpfm_events_option() which parses the
event string '{},{instructions}' and can not handle a leading empty
group notation '{},...'.

The code detects the first (empty) group indicator '{' but does not
terminate group processing on the following group closing character '}'.
So when the second group indicator '{' is detected, the code assumes
a nested group and returns an error.

With the error message fixed, also change the expected event number to
one for the test case to succeed.

While at it also fix a memory leak. In good case the function does not
free the duplicated string given as first parameter.

Output after:
 # ./perf test -F 63
 63: Test libpfm4 support                                            :
 63.1: test of individual --pfm-events                               :
 Error:
 failed to parse event stereolab : event not found
 Error:
 failed to parse event stereolab,instructions : event not found
 Error:
 failed to parse event instructions,stereolab : event not found
  Ok
 63.2: test groups of --pfm-events                                   :
 Error:
 failed to parse event {stereolab} : event not found
 Error:
 failed to parse event {instructions,cycles},{instructions,stereolab} : \
	 event not found
  Ok
 #
Error message 'nested event groups not supported' is gone.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-By: Ian Rogers <irogers@google.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20210517140931.2559364-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>