gpio: htc-egpio: Remove set but not used variable 'bit'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpio/gpio-htc-egpio.c: In function 'egpio_set':
drivers/gpio/gpio-htc-egpio.c:192:20: warning:
 variable 'bit' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>