tty: serial: 8250: 8250_port: Staticify functions referenced by pointers

Fixes the following W=1 kernel build warning(s):

 drivers/tty/serial/8250/8250_port.c:349:14: warning: no previous prototype for ‘au_serial_in’ [-Wmissing-prototypes]
 drivers/tty/serial/8250/8250_port.c:359:6: warning: no previous prototype for ‘au_serial_out’ [-Wmissing-prototypes]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Mike Hudson <Exoray@isys.ca>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/tty/serial/8250/8250_port.c

@@ -346,7 +346,7 @@ static const s8 au_io_out_map[8] = {
 	-1,	/* UART_SCR (unmapped) */
 };
 
-unsigned int au_serial_in(struct uart_port *p, int offset)
+static unsigned int au_serial_in(struct uart_port *p, int offset)
 {
 	if (offset >= ARRAY_SIZE(au_io_in_map))
 		return UINT_MAX;
@@ -356,7 +356,7 @@ unsigned int au_serial_in(struct uart_port *p, int offset)
 	return __raw_readl(p->membase + (offset << p->regshift));
 }
 
-void au_serial_out(struct uart_port *p, int offset, int value)
+static void au_serial_out(struct uart_port *p, int offset, int value)
 {
 	if (offset >= ARRAY_SIZE(au_io_out_map))
 		return;