ibmvnic: remove default label from to_string switch

This way the compiler warns when a new value is added to the enum but
not to the string translation like:

drivers/net/ethernet/ibm/ibmvnic.c: In function 'adapter_state_to_string':
drivers/net/ethernet/ibm/ibmvnic.c:832:2: warning: enumeration value 'VNIC_FOOBAR' not handled in switch [-Wswitch]
  switch (state) {
  ^~~~~~
drivers/net/ethernet/ibm/ibmvnic.c: In function 'reset_reason_to_string':
drivers/net/ethernet/ibm/ibmvnic.c:1935:2: warning: enumeration value 'VNIC_RESET_FOOBAR' not handled in switch [-Wswitch]
  switch (reason) {
  ^~~~~~

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Acked-by: Lijun Pan <lijunp213@gmail.com>
Link: https://lore.kernel.org/netdev/CAOhMmr701LecfuNM+EozqbiTxFvDiXjFdY2aYeKJYaXq9kqVDg@mail.gmail.com/


Signed-off-by: David S. Miller <davem@davemloft.net>