perf symbols: Remove needless checks for map->groups->machine

Its sufficient to check if map->groups is NULL before using it to get
->machine value.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-utiepyiv8b1tf8f79ok9d6j8@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>