mwifiex: don't clear cmd_sent flag in timeout handler

When command timeout occurs due to a firmware/hardware bug,
there is no chance of next command being successful. We will
keep cmd_sent flag on so that next command won't be sent to
firmware.

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>