rtc: fix potential race condition

rtc: fix potential race condition

RTC drivers must not return an error after device registration.

[[email protected]: coding-style fixes]
Signed-off-by: Alessandro Zummo <[email protected]>
Reported-by: Ales Novak <[email protected]>
Cc: Alexander Shiyan <[email protected]>
Cc: Atsushi Nemoto <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Srikanth Srinivasan <[email protected]>
Cc: Lee Jones <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>