rtc: rtc-twl: Remove lockdep related local_irq_enable()

Now that the irq is properly threaded (due to it needing i2c access)
we should also remove the local_irq_enable() call in twl_rtc_interrupt.
Testing this with Pandaboard, the RTC is still working.

[Reworked commit message -jstultz]
Signed-off-by: John Stultz <john.stultz@linaro.org>