dm: sparse: Annotate field with __rcu for checking

Annotate the map field with __rcu since this is a rcu pointer which is checked
by sparse.

Signed-off-by: Pranith Kumar <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm.c

···
 	 * Use dm_get_live_table{_fast} or take suspend_lock for
 	 * dereference.
 	 */
-	struct dm_table *map;
+	struct dm_table __rcu *map;
 
 	struct list_head table_devices;
 	struct mutex table_devices_lock;