s390/qeth: handle error from qeth_update_from_chp_desc()

Subsequent code relies on the values that qeth_update_from_chp_desc()
reads from the CHP descriptor. Rather than dealing with weird errors
later on, just handle it properly here.

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