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: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/ioctl.c

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 98d4ffe..08ac53c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3667,9 +3667,10 @@
 
 	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 @@
 
 	if (copy_to_user(arg, p, sizeof(*p)))
 		ret = -EFAULT;
-
+out:
 	kfree(p);
 	return ret;
 }