staging: wilc1000: use mutex lock to synchronized sending 'wid' cmd to firmware

Use mutex lock to protect the issuing of wid cmd to the firmware.
Currently the wid commands are synchronized by use of hif_workqueue work
queue.
Now, these changes are required to synchronize the access to wid
command, so the commands can be issued directly from cfg80211 context
and 'WILC_wq' thread.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>