i40e: Remove timer and task only if created

In some error scenarios, we may find ourselves trying to remove a
non-existent timer or worktask.  This causes the kernel some bit
of consternation, so don't do it.

Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>