rtc: rv3028: quiet maybe-unused variable warning

When CONFIG_OF is disabled then the matching table is not referenced.

Signed-off-by: Alexandre Belloni <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/rtc/rtc-rv3028.c

···
 	return 0;
 }
 
-static const struct of_device_id rv3028_of_match[] = {
+static const __maybe_unused struct of_device_id rv3028_of_match[] = {
 	{ .compatible = "microcrystal,rv3028", },
 	{ }
 };