tty: serial: bcm63xx_uart: include linux/io.h

Include linux/io.h which provides the definition for
__raw_{readl,writel}, this is not necessary on MIPS since there is an
implicit inclusion, but it is on ARM for instance.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/bcm63xx_uart.c

@@ -30,6 +30,7 @@
 #include <linux/serial.h>
 #include <linux/serial_core.h>
 #include <linux/serial_bcm63xx.h>
+#include <linux/io.h>
 
 #define BCM63XX_NR_UARTS	2