KVM: s390: coding style kvm_s390_gisa_init/clear()

The change helps to reduce line length and
increases code readability.

Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <20190131085247.13826-5-mimu@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>