drivers/leds/leds-gpio.c: use linux/gpio.h rather than asm/gpio.h

Direct usage of the asm include has long been deprecated by the
introduction of gpiolib.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>