s390/qeth: improve trace entries for MAC address (un)registration

Add the failed MAC address into the trace message. Also fix up one
format string to use %x instead of %u for the CARD_DEVID.

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