perf tools: Add a 'struct map_groups' pointer to 'struct map_symbol'

And fill it whenever we setup a a 'struct map_symbol', now we need to
use it, next cset.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-fzwfcnddenz1o7uj1fzw3g46@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/map_symbol.h

@@ -4,10 +4,12 @@
 
 #include <linux/types.h>
 
+struct map_groups;
 struct map;
 struct symbol;
 
 struct map_symbol {
+	struct map_groups *mg;
 	struct map    *map;
 	struct symbol *sym;
 };