mwifiex: cancel pending commands during host sleep

Sometimes we may end up downloading other commands when host
sleep is configured. This patch makes sure that pending
commands are cancelled and we stop queueing further commands
during host sleep.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>