staging: brcm80211: brcmfmac: Fixed issues with iscan

Disabling the interface doesn't terminate undergoing
iscan in FW. When the interface is enabled immediately,
first scan request is returning the stale scan results,
which are populated during the earlier iscan. These stale
scan results are causing random failures with chromium
auto test cases.

With this patch, iscan will be terminated in FW whenever
iscan thread is terminated by the host driver.

Signed-off-by: Sukesh Srikakula <sukeshs@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>