ext4: release donor reference when EXT4_IOC_MOVE_EXT ioctl fails

When the EXT4_IOC_MOVE_EXT ioctl() fails on bigalloc file systems, we
should jump to the 'mext_out' label to release the donor file reference.
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ioctl.c

@@ -258,7 +258,8 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			       EXT4_FEATURE_RO_COMPAT_BIGALLOC)) {
 			ext4_msg(sb, KERN_ERR,
 				 "Online defrag not supported with bigalloc");
-			return -EOPNOTSUPP;
+			err = -EOPNOTSUPP;
+			goto mext_out;
 		}
 
 		err = mnt_want_write_file(filp);