ice: handle the VF VSI rebuild failure

VSI rebuild can be failed for LAN queue config, then the VF's VSI will
be NULL, the VF reset should be stopped with the VF entering into the
disable state.

Fixes: 12bb018c

 ("ice: Refactor VF reset")
Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>