[media] atmel-isi: Fix bad usage of IS_ERR_VALUE

IS_ERR_VALUE() assumes that its parameter is an unsigned long.
It can not be used to check if an unsigned int reflects an error.
Doing so can result in the following build warning.

drivers/media/platform/soc_camera/atmel-isi.c:
	In function "atmel_isi_probe":
	include/linux/err.h:21:38: warning:
		comparison is always false due to limited range of data type
drivers/media/platform/soc_camera/atmel-isi.c:1089:6: note:
	in expansion of macro "IS_ERR_VALUE"

If that warning is seen, the return value from platform_get_irq() is not
checked for errors.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>