ice: Forbid trusted VFs in switchdev mode

Merge issues caused the check for switchdev mode has been inserted
in wrong place. It should be in ice_set_vf_trust not in ice_set_vf_mac.

Trusted VFs are forbidden in switchdev mode because they should
be configured only from the host side.

Fixes: 1c54c839

 ("ice: enable/disable switchdev when managing VFs")
Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>