serial: sh-sci: Drop unused include

The sh-sci.h file includes the legacy <linux/gpio.h> header
but the driver is actually migrated to use the mctrl_gpio
library so this is not needed.

Cc: George G. Davis <george_davis@mentor.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200415180250.221762-1-linus.walleij@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>