ibmvnic: Fix statistics buffers memory leak

Move initialization of statistics buffers from ibmvnic_init function
into ibmvnic_probe. In the current state, ibmvnic_init will be called
again during a device reset, resulting in the allocation of new
buffers without freeing the old ones.

Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>