mwifiex: replace num_cmd_timeout with is_cmd_timedout

Command timeout happens when firmware goes into bad state.
There is no chance that next command will be successful after
this. Hence we will maintain a flag instead of count.

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>