nfc: pn533: mark OF device ID tables as maybe unused

The driver can match either via OF or I2C ID tables.  If OF is disabled,
the table will be unused:

    drivers/nfc/pn533/i2c.c:252:34: warning:
        ‘of_pn533_i2c_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210528124200.79655-7-krzysztof.kozlowski@canonical.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/nfc/pn533/i2c.c

@@ -249,7 +249,7 @@ static int pn533_i2c_remove(struct i2c_client *client)
 	return 0;
 }
 
-static const struct of_device_id of_pn533_i2c_match[] = {
+static const struct of_device_id of_pn533_i2c_match[] __maybe_unused = {
 	{ .compatible = "nxp,pn532", },
 	/*
 	 * NOTE: The use of the compatibles with the trailing "...-i2c" is