ibmvnic: Define vnic_login_client_data name field as unsized array

The "name" field of struct vnic_login_client_data is a char array of
undefined length. This should be written as "char name[]" so the compiler
can make better decisions about the field (for example, not assuming
it's a single character). This was noticed while trying to tighten the
CONFIG_FORTIFY_SOURCE checking.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>