gpiolib: remove unused variable

This was left behind by a cleanup patch:

drivers/gpio/gpiolib.c: In function 'gpiochip_irqchip_init_valid_mask':
drivers/gpio/gpiolib.c:1474:6: error: unused variable 'i' [-Werror=unused-variable]

Fixes: 923a654c186c ("gpiolib: Re-use bitmap_fill() instead of open coded loop")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Colin King <colin.king@canonical.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -1471,8 +1471,6 @@ static struct gpio_chip *find_chip_by_name(const char *name)
 
 static int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gpiochip)
 {
-	int i;
-
 	if (!gpiochip->irq_need_valid_mask)
 		return 0;