serial: lpc32xx_hs: Drop surplus include

The driver includes <linux/gpio.h> but does not use any symbols
from the file so drop this include.

Cc: Roland Stigge <stigge@antcom.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20200415184300.269889-1-linus.walleij@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/lpc32xx_hs.c

@@ -23,7 +23,6 @@
 #include <linux/nmi.h>
 #include <linux/io.h>
 #include <linux/irq.h>
-#include <linux/gpio.h>
 #include <linux/of.h>
 #include <linux/sizes.h>
 #include <linux/soc/nxp/lpc32xx-misc.h>