perf maps: Add missing unlock to maps__insert() error case

`tools/perf/util/map.c` has a function named `maps__insert` that
acquires a write lock if its in multithread context.

Even though this lock is released when function successfully completes,
there's a branch that is executed when `maps_by_name == NULL` that
returns from this function without releasing the write lock.

Added an `up_write` to release the lock when this happens.

Fixes: a7c2b572e2 ("perf map_groups: Auto sort maps by name, if needed")
Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/20200120141553.23934-1-cengiz@kernel.wtf
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/map.c

@@ -549,6 +549,7 @@ void maps__insert(struct maps *maps, struct map *map)
 
 			if (maps_by_name == NULL) {
 				__maps__free_maps_by_name(maps);
+				up_write(&maps->lock);
 				return;
 			}