media: samsung: exynos4-is: do not require pinctrl

Driver does not handle pin configuration switching and several DTS
provide empty pinctrl property, just to satisfy the driver's requirement
for it.  Drop requirement for pinctrl property as it is really optional.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>