Staging: atomisp: fix locking in alloc_user_pages()

We call this function with the lock held and should also return with the
lock held as well.  This one error path is not-consistent because we
should return without the lock held.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>