[media] mt9p031: Include linux/of.h header

'of_match_ptr' is defined in linux/of.h. Include it explicitly to
avoid build breakage in the future.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/i2c/mt9p031.c

@@ -19,6 +19,7 @@
 #include <linux/i2c.h>
 #include <linux/log2.h>
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/of_gpio.h>
 #include <linux/pm.h>
 #include <linux/regulator/consumer.h>