wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/block/ioctl.c b/block/ioctl.c
index 2c84683..77f5d177 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -455,12 +455,12 @@
 	if (arg && !blkdev_dax_capable(bdev))
 		return -ENOTTY;
 
-	mutex_lock(&bdev->bd_inode->i_mutex);
+	inode_lock(bdev->bd_inode);
 	if (bdev->bd_map_count == 0)
 		inode_set_flags(bdev->bd_inode, arg, S_DAX);
 	else
 		rc = -EBUSY;
-	mutex_unlock(&bdev->bd_inode->i_mutex);
+	inode_unlock(bdev->bd_inode);
 	return rc;
 }
 #else