gpio: merrifield: Remove unused header

I don't remember how linux/gpio.h made the source, now it seems unused.
Remove it.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-merrifield.c

@@ -11,7 +11,6 @@
 
 #include <linux/bitops.h>
 #include <linux/gpio/driver.h>
-#include <linux/gpio.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>