perf dwarf-aux: Fix off-by-one in die_get_varname()

perf dwarf-aux: Fix off-by-one in die_get_varname()

The die_get_varname() returns "(unknown_type)" string if it failed to
find a type for the variable.  But it had a space before the opening
parenthesis and it made the closing parenthesis cut off due to the
off-by-one in the string length (14).

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Fixes: 88fd633cdfa19060 ("perf probe: No need to use formatting strbuf method")
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230612234102.3909116-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>