[media] atmel-isi: Fix a truncate warning

   drivers/media/platform/soc_camera/atmel-isi.c: In function 'start_streaming':
   drivers/media/platform/soc_camera/atmel-isi.c:397:26: warning: large integer implicitly truncated to unsigned type [-Woverflow]
     isi_writel(isi, ISI_INTDIS, ~0UL);
                             ^

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>