video: da8xx: Register IRQ as last thing in driver probing.

Following commit exposed a bug in driver:

	"fbdev: da8xx/omap-l1xx: implement double buffering"

Bug is, if interrupt handler is called before initialization is
finished, raster controller is enabled and following register
modifications causes hardware to stay in a broken state.

By looking at this one may say that proper locking is missing in
this driver, and a more proper fix should be prepared. However,
aformentioned commit causes a regression in the driver and some
fix to current one should be applied first.

Signed-off-by: Caglar Akyuz <caglar@bilkon-kontrol.com.tr>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>