fs: Add helper to clean bdev aliases under a bh and use it

Add a helper function that clears buffer heads from a block device
aliasing passed bh. Use this helper function from filesystems instead of
the original unmap_underlying_metadata() to save some boiler plate code
and also have a better name for the functionalily since it is not
unmapping anything for a *long* time.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

fs/ufs/inode.c

@@ -1070,8 +1070,7 @@ static int ufs_alloc_lastblock(struct inode *inode, loff_t size)
 
        if (buffer_new(bh)) {
 	       clear_buffer_new(bh);
-	       unmap_underlying_metadata(bh->b_bdev,
-					 bh->b_blocknr);
+	       clean_bdev_bh_alias(bh);
 	       /*
 		* we do not zeroize fragment, because of
 		* if it maped to hole, it already contains zeroes