staging: atomisp: fix unsigned int comparison with less than zero

Fix warnings from the smatch tool

atomisp_cmd.c:2649
  atomisp_set_array_res() warn:
  unsigned 'config->width' is never less than zero.

atomisp_cmd.c:2650
  atomisp_set_array_res() warn:
  unsigned 'config->height' is never less than zero.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>