regulator: arizona-micsupp: Delete unused include

This driver uses no symbols from <linux/gpio.h> so just drop
this include.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/arizona-micsupp.c

@@ -16,7 +16,6 @@
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>
 #include <linux/regulator/of_regulator.h>
-#include <linux/gpio.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 #include <sound/soc.h>