rtc: sirfsoc: Make sysrtc_regmap_config static

Fix sparse warning:

drivers/rtc/rtc-sirfsoc.c:282:28: warning:
 symbol 'sysrtc_regmap_config' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-sirfsoc.c

@@ -279,7 +279,7 @@ static const struct of_device_id sirfsoc_rtc_of_match[] = {
 	{},
 };
 
-const struct regmap_config sysrtc_regmap_config = {
+static const struct regmap_config sysrtc_regmap_config = {
 	.reg_bits = 32,
 	.val_bits = 32,
 	.fast_io = true,