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 <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/ioctl.c

···
 			       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);