staging: ath6kl: Eliminate cfg80211 warnings

Cancel the pending scan operation once the interface is going down to
avoid warnings from the cfg80211 module. Once the interface is down,
cfg80211 checks for any pending scan requests and dumps a warning if it
finds one. It expects the driver to abort any ongoing scan operation
once the driver detects that the interface is going down.

Signed-off-by: Vipin Mehta <vmehta@atheros.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>