wifi: iwlwifi: Fix error code in iwl_op_mode_dvm_start()

wifi: iwlwifi: Fix error code in iwl_op_mode_dvm_start()

Preserve the error code if iwl_setup_deferred_work() fails.  The current
code returns ERR_PTR(0) (which is NULL) on this path.  I believe the
missing error code potentially leads to a use after free involving
debugfs.

Fixes: 90a0d9f33996 ("iwlwifi: Add missing check for alloc_ordered_workqueue")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/a7a1cd2c-ce01-461a-9afd-dbe535f8df01@sabinyo.mountain
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>