MIPS: ralink: Remove unused of_gpio.h

of_gpio.h is deprecated and subject to remove.
The driver doesn't use it, simply remove the unused header.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/ralink/timer.c

@@ -9,7 +9,6 @@
 #include <linux/platform_device.h>
 #include <linux/interrupt.h>
 #include <linux/timer.h>
-#include <linux/of_gpio.h>
 #include <linux/clk.h>
 
 #include <asm/mach-ralink/ralink_regs.h>