gpio: bt8xx: Include proper header

This driver has no business including <linux/gpio.h>, it is a
driver so include <linux/gpio/driver.h>.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-bt8xx.c

@@ -46,7 +46,7 @@
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/spinlock.h>
-#include <linux/gpio.h>
+#include <linux/gpio/driver.h>
 #include <linux/slab.h>
 
 /* Steal the hardware definitions from the bttv driver. */