wlan: Free cached channel list with restore channels

When driver receives the command to disable the channels
it maintains a list of the channels which are disabled.
During SAP stop, driver restores the disabled channels
but it is not freeing the cache list. Now when again the
command is issued to disable the channels, driver is not
processing this command as it still has the channels in its
cached list which were disabled during previous command.
This results into failure of current command and all the
subsequent commands to disable the channels until the
cache list is not cleared with set_disable_channel_list
command with empty channel list.
To address above issue, clear the cache channel list
as soon as driver restores the channels on stop bss.

Change-Id: I6b8c7ba250ef38b892ab83621add45fbfc09a2cd
CRs-fixed: 2712499