qcacmn: Flush the PCIe window select config before device access

PCIe window select config reg update goes on different NoC and
actual PCIe device register access goes on the different NoC.
If there is delay in window select reg config, it can result in
access some other PCIe IO memory access and will result in actual
register write lost issue. Make sure to flush the window select
reg write before actual device reg access.

Change-Id: I1fe17aad7ae8fd5dea7a618273d9cd813b236a85
CRs-Fixed: 2687676