Staging: atomisp: fix an uninitialized variable bug

There are some error paths in atomisp_css_frame_allocate() which don't
initialize "res" so it could lead us to try release random memory.

Fixes: a49d2536

 ("staging/atomisp: Add support for the Intel IPU v2")
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>