pinctrl: armada-37xx: remove unused variable

A cleanup left behind a temporary variable that is now unused:

drivers/pinctrl/mvebu/pinctrl-armada-37xx.c: In function 'armada_37xx_irq_startup':
drivers/pinctrl/mvebu/pinctrl-armada-37xx.c:693:20: error: unused variable 'chip' [-Werror=unused-variable]

This removes the declarations as well.

Fixes: 3ee9e605

 ("pinctrl: armada-37xx: Stop using struct gpio_chip.irq_base")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>