wl12xx: set the irq polarity before loading the fw

The polarity should be set before the firmware is loaded
since the firmware touches the same register. Access
of the firmware and driver to the same register will
cause a collision since there is no exclusion scheme.

Signed-off-by: Yoni Divinsky <yoni.divinsky@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>