s390/qeth: clean up card initialization

The qeth_card struct is kzalloc-ed, so remove all the redundant
0-initializations. While at it, split up what's left of
qeth_determine_card_type().

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>