pinctrl: mediatek: remove set but not used variable 'e'

drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c: In function mtk_hw_pin_field_lookup:
drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c:70:39: warning:
 variable e set but not used [-Wunused-but-set-variable]

Since commit 3de7deef

 ("pinctrl: mediatek: Check gpio pin
number and use binary search in mtk_hw_pin_field_lookup()"),
it is not used any more, so remove it, also remove redundant
assignment to variable c, it will be assigned a new value later
before used.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20200218023625.14324-1-yuehaibing@huawei.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>