s390/qeth: use __ipa_cmd() for casting an IPA cmd buffer

"s390/qeth: fix SETIP command handling" introduced a new helper, apply
it driver-wide.

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