mwifiex: cancel pending scan during disconnect

It is obeserved that sometimes scan operation will block the disconnect
during system suspend. It's ok to cancel ongoing scan in this case. It
reduces unnecessary system suspend delay.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>