tty: serial: amba-pl011: Mark 'sbsa_uart_acpi_match' as __maybe_unused

When !ACPI 'sbsa_uart_acpi_match' is not referenced.

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

 drivers/tty/serial/amba-pl011.c:2792:36: warning: ‘sbsa_uart_acpi_match’ defined but not used [-Wunused-const-variable=]

Cc: Russell King <linux@armlinux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104193549.4026187-18-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -2789,7 +2789,7 @@ static const struct of_device_id sbsa_uart_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, sbsa_uart_of_match);
 
-static const struct acpi_device_id sbsa_uart_acpi_match[] = {
+static const struct acpi_device_id __maybe_unused sbsa_uart_acpi_match[] = {
 	{ "ARMH0011", 0 },
 	{},
 };