perf thread: Rename thread->mg to thread->maps

One more step on the merge of 'struct maps' with 'struct map_groups'.

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-69vcr8pubpym90skxhmbwhiw@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/unwind-libdw.c

@@ -200,7 +200,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
 	struct unwind_info *ui, ui_buf = {
 		.sample		= data,
 		.thread		= thread,
-		.machine	= thread->mg->machine,
+		.machine	= thread->maps->machine,
 		.cb		= cb,
 		.arg		= arg,
 		.max_stack	= max_stack,