i40e: remove logically dead code

This patch removes the !vf condition check that cannot be
true in i40e_ndo_set_vf_trust function

Detected by CoverityScan, CID 1397531 Logically dead code

Signed-off-by: Lihong Yang <lihong.yang@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>