mwifiex: check driver status in connect and scan handlers

Ignore scan and connection requests from cfg80211 when driver
unload is in process or previous command has timed out due to
a firmware bug. This patch fixes corner case system crash
issues.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>