wilc1000: add 'initialized' flag check before adding an element to TX queue

Add 'initialized' variable check before adding net/mgmt packet to TX queue
as safety check before passing the commands to the firmware.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210916164902.74629-10-ajay.kathat@microchip.com