iavf: Fix error handling in iavf_init_module()

The iavf_init_module() won't destroy workqueue when pci_register_driver()
failed. Call destroy_workqueue() when pci_register_driver() failed to
prevent the resource leak.

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

Fixes: 2803b16c

 ("i40e/i40evf: Use private workqueue")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>