whack-a-mole: don't open-code iminor/imajor

several instances creeped back into the tree...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index e5ff328..b513300 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -663,7 +663,7 @@ static inline int is_loop_device(struct file *file)
 {
 	struct inode *i = file->f_mapping->host;
 
-	return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
+	return i && S_ISBLK(i->i_mode) && imajor(i) == LOOP_MAJOR;
 }
 
 static int loop_validate_file(struct file *file, struct block_device *bdev)