serial: 8250_mtk: make two read-only arrays static const

Don't populate the read-only arrays fraction_L_mapping and
fraction_M_mapping on the stack but instead make them static
const. Also makes the object code a little smaller.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220307230055.168241-1-colin.i.king@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ColinIanKing

drivers/tty/serial/8250/8250_mtk.c

@@ -289,10 +289,10 @@ static void
 mtk8250_set_termios(struct uart_port *port, struct ktermios *termios,
 			struct ktermios *old)
 {
-	unsigned short fraction_L_mapping[] = {
+	static const unsigned short fraction_L_mapping[] = {
 		0, 1, 0x5, 0x15, 0x55, 0x57, 0x57, 0x77, 0x7F, 0xFF, 0xFF
 	};
-	unsigned short fraction_M_mapping[] = {
+	static const unsigned short fraction_M_mapping[] = {
 		0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 3
 	};
 	struct uart_8250_port *up = up_to_u8250p(port);