revert "rtc: cdev lock_kernel() pushdown"

Revert commit 51a776fa

 ("rtc: cdev
lock_kernel() pushdown").  The RTC framework does not need BKL
protection.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alessandro Zummo <alessandro.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>