mwifiex: mask PCIe interrupts before removal

The PCIe driver didn't mask the host interrupts before trying to tear
down. This causes lockups at reboot or rmmod when using MSI-X on 8997,
since the MSI handler gets confused and locks up the system.

Also tested on 8897, which does not support MSI-X (and wasn't
experiencing this same bug). No regressions seen there.

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