rtc: gamecube: Add missing iounmap in gamecube_rtc_read_offset_from_sram

The hw_srnprot needs to be unmapped when gamecube_rtc_read_offset_from_sram returns.

Fixs: 86559400 (rtc: gamecube: Add a RTC driver for the GameCube, Wii and Wii U)
Signed-off-by: Yuan Can <yuancan@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220511071354.46202-1-yuancan@huawei.com

drivers/rtc/rtc-gamecube.c

@@ -267,6 +267,7 @@ static int gamecube_rtc_read_offset_from_sram(struct priv *d)
 	ret = regmap_read(d->regmap, RTC_SRAM_BIAS, &d->rtc_bias);
 	if (ret) {
 		pr_err("failed to get the RTC bias\n");
+		iounmap(hw_srnprot);
 		return -1;
 	}