perf debug: fix hex dump partial final line

perf debug: fix hex dump partial final line

The loop counter math in trace_event was much more complicated than
necessary, resulting in incorrectly decoding the human-readable
portion of the partial last line of hexdump in "perf trace -D" output:

.  0020:  00 00 00 00 00 00 00 00 2f 73 62 69 6e 2f 69 6e  ......../sbin/i
.  0030:  69 74 00 00 00 00 00 00                          /sbin/i

With this fixed (and simpler!) code, we get the correct output:

.  0020:  00 00 00 00 00 00 00 00 2f 73 62 69 6e 2f 69 6e  ......../sbin/in
.  0030:  69 74 00 00 00 00 00 00                          it......

Cc: Ingo Molnar <mingo@elte.hu>
LPU-Reference: <20100612024404.GA24469@hexapodia.org>
Signed-off-by: Andy Isaacson <adi@hexapodia.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>