serial: blackfin: Fix missing gpio.h

If CONFIG_SERIAL_BFIN_CTSRTS is set, compile fails because of missing
declarations for the gpio_* api. Include necessary header.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/bfin_sport_uart.c

@@ -33,6 +33,7 @@
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
 #include <linux/serial_core.h>
+#include <linux/gpio.h>
 
 #include <asm/bfin_sport.h>
 #include <asm/delay.h>