mwifiex: pcie: unify MSI-X / non-MSI-X interrupt process

After removing the interrupt loop in commit 5d5ddb5e ("mwifiex:
pcie: don't loop/retry interrupt status checks"), there is practically
zero difference between mwifiex_process_pcie_int() (which handled legacy
PCI interrupts and MSI interrupts) and mwifiex_process_msix_int() (which
handled MSI-X interrupts). Let's add the one relevant line to
mwifiex_process_pcie_int() and kill the copy-and-paste.

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