ixgbevf: Fix resource leak in ixgbevf_init_module()

ixgbevf_init_module() won't destroy the workqueue created by
create_singlethread_workqueue() when pci_register_driver() failed. Add
destroy_workqueue() in fail path to prevent the resource leak.

Similar to the handling of u132_hcd_init in commit f276e002
("usb: u132-hcd: fix resource leak")

Fixes: 40a13e24

 ("ixgbevf: Use a private workqueue to avoid certain possible hangs")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Reviewed-by: Saeed Mahameed <saeed@kernel.org>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>