ARM: OMAP: smartreflex: fix IRQ handling bug

Fix a bug which has been on this driver since
it was added by the original commit 984aa6db
which would never clear IRQSTATUS bits.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>
Cc: stable@vger.kernel.org
Signed-off-by: Tony Lindgren <tony@atomide.com>