ibmvnic: fix kernel build warning

drivers/net/ethernet/ibm/ibmvnic.c: In function ‘adapter_state_to_string’:
drivers/net/ethernet/ibm/ibmvnic.c:855:2: warning: enumeration value ‘VNIC_DOWN’ not handled in switch [-Wswitch]
  855 |  switch (state) {
      |  ^~~~~~
drivers/net/ethernet/ibm/ibmvnic.c: In function ‘reset_reason_to_string’:
drivers/net/ethernet/ibm/ibmvnic.c:1958:2: warning: enumeration value ‘VNIC_RESET_PASSIVE_INIT’ not handled in switch [-Wswitch]
 1958 |  switch (reason) {
      |  ^~~~~~

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>