rtc: pl031: fix rtc features null pointer dereference

In the Linux kernel, the following vulnerability has been resolved: rtc: pl031: fix rtc features null pointer dereference When there is no interrupt line, rtc alarm feature is disabled. The clearing of the alarm feature bit was being done prior to allocations of ldata->rtc device, resulting in a null pointer dereference. Clear RTC_FEATURE_ALARM after the rtc device is allocated.