wifi: rtw88: check the return value of alloc_workqueue()

The function alloc_workqueue() in rtw_core_init() can fail, but
there is no check of its return value. To fix this bug, its return value
should be checked with new error handling code.

Fixes: fe101716

 ("rtw88: replace tx tasklet with work queue")
Reported-by: Hacash Robot <hacashRobot@santino.com>
Signed-off-by: William Dean <williamsukatube@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220723063756.2956189-1-williamsukatube@163.com