perf report: Set proper sort__mode for the branch option

perf report: Set proper sort__mode for the branch option

When you specify "--branch-stack"("-b" for short) or
"--no-branch-stack", "branch_mode" variable is set to 1 or 0
respectively. However, the code is just checking if the variable is -1
or not, ignoring "branch_mode == 1" case. Thus "perf report -b" dose not
show its result with the branch sorted mode. This patch fix the problem.

Signed-off-by: Naohiro Aota <naota@elisp.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/87y4v1fylq.fsf@elisp.net
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>