KVM: s390: Fix user triggerable bug in dead code

KVM: s390: Fix user triggerable bug in dead code

commit 614a80e474b227cace52fd6e3c790554db8a396e upstream.

In the early days, we had some special handling for the
KVM_EXIT_S390_SIEIC exit, but this was gone in 2009 with commit
d7b0b5eb3000 (KVM: s390: Make psw available on all exits, not
just a subset).

Now this switch statement is just a sanity check for userspace
not messing with the kvm_run structure. Unfortunately, this
allows userspace to trigger a kernel BUG. Let's just remove
this switch statement.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>