net-next: mediatek: don't use intermediate variables to store IRQ masks

The code currently uses variables to store and never modify the bit masks
of interrupts. This is legacy code from an early version of the driver
that supported MIPS based SoCs where the IRQ bits depended on the actual
SoC. As the bits are the same for all ARM based SoCs using this driver we
can remove the intermediate variables.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>