mwifiex: process event before command response

During extended scan, SCAN report event is always followed by
command response. Sometimes It is observed that command response
is processed before SCAN report which leads to a crash, because
current command node is cleared while handling the response.
This patch makes sure that driver's main thread gives priority
to events over command responses.

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