wifi: libertas: fix memory leak in lbs_init_adapter()

When kfifo_alloc() failed in lbs_init_adapter(), cmd buffer is not
released. Add free memory to processing error path.

Fixes: 7919b89c ("libertas: convert libertas driver to use an event/cmdresp queue")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221208121448.2845986-1-shaozhengchao@huawei.com