serial: sunzilog: Mark sunzilog_putchar() __maybe_unused

If CONSOLE_POLL=n, CONFIG_SERIAL_SUNZILOG_CONSOLE=n, and CONFIG_SERIO=m:

    drivers/tty/serial/sunzilog.c:1128:13: error: ‘sunzilog_putchar’ defined but not used [-Werror=unused-function]
     1128 | static void sunzilog_putchar(struct uart_port *port, int ch)
	  |             ^~~~~~~~~~~~~~~~

Fix this by marking sunzilog_putchar() __maybe_unused.
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20211026080426.2444756-1-geert@linux-m68k.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sunzilog.c

@@ -1125,7 +1125,7 @@ static void sunzilog_free_tables(void)
 
 #define ZS_PUT_CHAR_MAX_DELAY	2000	/* 10 ms */
 
-static void sunzilog_putchar(struct uart_port *port, int ch)
+static void __maybe_unused sunzilog_putchar(struct uart_port *port, int ch)
 {
 	struct zilog_channel __iomem *channel = ZILOG_CHANNEL_FROM_PORT(port);
 	int loops = ZS_PUT_CHAR_MAX_DELAY;