mwifiex: pcie: remove unnecessary masks

After removing the interrupt loop in commit 5d5ddb5e ("mwifiex:
pcie: don't loop/retry interrupt status checks"), we don't need to keep
track of the cleared interrupts (actually, we didn't need to do that
before, but we *really* don't need to now).

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>