ALSA: atmel: remove dependency on <mach/gpio.h>

This include is completely unused since the AT91 sound driver
actually uses gpiolib properly.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>