wifi: iwl3945: Add missing check for create_singlethread_workqueue

wifi: iwl3945: Add missing check for create_singlethread_workqueue

[ Upstream commit 25ae2d1000e61940f2a470f0a622c2b0cb6299a1 ]

Add the check for the return value of the create_singlethread_workqueue
in order to avoid NULL pointer dereference.

Fixes: f71f97212c63 ("[IWLWIFI]: add iwlwifi wireless drivers")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230208063032.42763-2-jiasheng@iscas.ac.cn
Signed-off-by: Sasha Levin <sashal@kernel.org>