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

drivers/tty/serial/sh-sci.h

@@ -2,7 +2,6 @@
 #include <linux/bitops.h>
 #include <linux/serial_core.h>
 #include <linux/io.h>
-#include <linux/gpio.h>
 
 #define SCI_MAJOR		204
 #define SCI_MINOR_START		8