btrfs: fix error pointer dereference in btrfs_ioctl_rm_dev_v2()

btrfs: fix error pointer dereference in btrfs_ioctl_rm_dev_v2()

commit d815b3f2f273537cb8afaf5ab11a46851f6c03e5 upstream.

If memdup_user() fails the error handing will crash when it tries
to kfree() an error pointer.  Just return directly because there is
no cleanup required.

Fixes: 1a15eb724aae ("btrfs: use btrfs_get_dev_args_from_path in dev removal ioctls")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>