staging: wilc1000: move the allocation of cmd out of wilc_enqueue_cmd()

Instead of allocating the host_if_cmd in wilc_enqueue_cmd() now moved
the allocation of cmd in the caller. Added the NULL check for
'hif_workqueue' before posting the work queue in wilc_enqueue_cmd().
Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>