gpio: lpc32xx: 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: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-lpc32xx.c

@@ -21,6 +21,7 @@
 #include <linux/io.h>
 #include <linux/errno.h>
 #include <linux/gpio.h>
+#include <linux/of.h>
 #include <linux/of_gpio.h>
 #include <linux/platform_device.h>
 #include <linux/module.h>