rtc-at32ap700x: fix irq init oops

Reorder at32_rtc_probe() so that it's safe (no oopsing) to fire the
IRQ handler the instant that it's registered.  (Bug noted via "Debug
shared IRQ handlers" kernel debug option.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: <hcegtvedt@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>