nfc: st21nfca: mark ACPI and OF device ID tables as maybe unused

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

    drivers/nfc/st21nfca/i2c.c:593:34: warning:
        ‘of_st21nfca_i2c_match’ defined but not used [-Wunused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210528124200.79655-11-krzysztof.kozlowski@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/nfc/st21nfca/i2c.c

@@ -584,13 +584,13 @@ static const struct i2c_device_id st21nfca_hci_i2c_id_table[] = {
 };
 MODULE_DEVICE_TABLE(i2c, st21nfca_hci_i2c_id_table);
 
-static const struct acpi_device_id st21nfca_hci_i2c_acpi_match[] = {
+static const struct acpi_device_id st21nfca_hci_i2c_acpi_match[] __maybe_unused = {
 	{"SMO2100", 0},
 	{}
 };
 MODULE_DEVICE_TABLE(acpi, st21nfca_hci_i2c_acpi_match);
 
-static const struct of_device_id of_st21nfca_i2c_match[] = {
+static const struct of_device_id of_st21nfca_i2c_match[] __maybe_unused = {
 	{ .compatible = "st,st21nfca-i2c", },
 	{ .compatible = "st,st21nfca_i2c", },
 	{}