Btrfs: don't leak ioctl args in btrfs_ioctl_dev_replace

struct btrfs_ioctl_dev_replace_args memory is leaked if replace is
requested on a read-only filesystem.  Fix it.
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <chris.mason@fusionio.com>

fs/btrfs/ioctl.c

@@ -3667,9 +3667,10 @@ static long btrfs_ioctl_dev_replace(struct btrfs_root *root, void __user *arg)
 
 	switch (p->cmd) {
 	case BTRFS_IOCTL_DEV_REPLACE_CMD_START:
-		if (root->fs_info->sb->s_flags & MS_RDONLY)
-			return -EROFS;
-
+		if (root->fs_info->sb->s_flags & MS_RDONLY) {
+			ret = -EROFS;
+			goto out;
+		}
 		if (atomic_xchg(
 			&root->fs_info->mutually_exclusive_operation_running,
 			1)) {
@@ -3695,7 +3696,7 @@ static long btrfs_ioctl_dev_replace(struct btrfs_root *root, void __user *arg)
 
 	if (copy_to_user(arg, p, sizeof(*p)))
 		ret = -EFAULT;
-
+out:
 	kfree(p);
 	return ret;
 }