mx28: fix clearing of IRQs in power init

mx28: fix clearing of IRQs in power init

There are 2 locations in the power init code for the mx28 where IRQs are not being cleared because incorrect methods to clear those bits were being used.  This was causing my board to get stuck waiting for POWER_CTRL_VDD5V_DROOP_IRQ to clear.  Using the correct method to clear the IRQs fixes it.

Signed-off-by: Zach Sadecki <zach@itwatchdogs.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Acked-by: Marek Vasut <marek.vasut@gmail.com>