rtc: Remove BKL from efirtc

BKL locking came to efirtc via the big BKL push down, but the access
to the efi functions is protected by efi_rtc_lock already.

Remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091010153350.046644063@linutronix.de>