serial: make local functions static

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/drivers/serial/serial_sh.c b/drivers/serial/serial_sh.c
index 144a925..7c1f271 100644
--- a/drivers/serial/serial_sh.c
+++ b/drivers/serial/serial_sh.c
@@ -122,7 +122,7 @@
 	sci_out(&sh_sci, SCLSR, 0x00);
 }
 
-void serial_raw_putc(const char c)
+static void serial_raw_putc(const char c)
 {
 	while (1) {
 		/* Tx fifo is empty */
@@ -152,7 +152,7 @@
 }
 
 
-int serial_getc_check(void)
+static int serial_getc_check(void)
 {
 	unsigned short status;