rtc: pl031: fix resource leak in pl031_probe

When devm_rtc_allocate_device is failed in pl031_probe, it should release
mem regions with device.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Liang <zhengliang6@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201112093139.32566-1-zhengliang6@huawei.com