mwifiex: disable auto deep sleep before unloading the driver

Since the auto deep sleep mode has been enabled at driver init time
we should disable it at driver unloading to shutdown the function
gracefully.

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>