perf tools: Fix the code to strip command name

perf tools: Fix the code to strip command name

Recent commit broke command name strip in perf_event__get_comm_ids
function. It replaced left to right search for '\n' with rtrim, which
actually does right to left search. It occasionally caught earlier '\n'
and kept trash in the command name.

Keeping the ltrim, but moving back the left to right '\n' search
instead of the rtrim.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Taeung Song <treeze.taeung@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yao Jin <yao.jin@linux.intel.com>
Fixes: e8677d9b33c6 ("perf tools: Refactor the code to strip command name with {l,r}trim()")
Link: http://lkml.kernel.org/r/20170420092430.29657-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>