When removing rtc-cmos, we get a WARN, because it tries to remove a driver it could not register successfully or did not try to register at all. The patch below fixes the problem. http://patchwork.kernel.org/patch/34089/
commit 659098141d02eb8e3545be8969d262e02d2f3f98 "rtc: mark if rtc-cmos drivers were successfully registered"