s390x/kvm: Fix coding style in handle_sigp()

To make scripts/checkpatch.pl happy for the following patches,
the coding style in handle_sigp() has to be fixed first.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
