qcacmn: Cleanup reg_cache_channel_state

Cleanup reg_cache_channel_state and the
related code with it.
Also, changed the logic so as to compare
channel freq instead of channel number in
reg_modify_chan_list_for_cached_channels()

Change-Id: I424b6886ed18f73bae0d2b36e36a9ddc1819688b
CRs-Fixed: 2908016