qcacld-3.0: Fix combined weight issue in ACS

Currently the driver calculates the best channel
amoung the given spectrum and uses logic to select
best frequency amoung the BW members, but the logic
to maximize the weight before selecting the min
weight is wrong, and must be done after the selection
of the minimum weight frequency.

Fix is to maximize the weight after the minimum weight
channel is selected.

Change-Id: Ie196462fbcc4215e6eb655168d07305110ff0ee7
CRs-Fixed: 2578582