btrfs: use cond_resched_rwlock_write() during inode eviction

At evict_inode_truncate_pages(), instead of manually checking if
rescheduling is needed, then unlock the extent map tree, reschedule and
then write lock again the tree, use the helper cond_resched_rwlock_write()
which does all that.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -5305,11 +5305,7 @@ static void evict_inode_truncate_pages(struct inode *inode)
 		clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
 		remove_extent_mapping(map_tree, em);
 		free_extent_map(em);
-		if (need_resched()) {
-			write_unlock(&map_tree->lock);
-			cond_resched();
-			write_lock(&map_tree->lock);
-		}
+		cond_resched_rwlock_write(&map_tree->lock);
 	}
 	write_unlock(&map_tree->lock);