KVM: s390: pv: refactoring of kvm_s390_pv_deinit_vm

KVM: s390: pv: refactoring of kvm_s390_pv_deinit_vm

Refactor kvm_s390_pv_deinit_vm to improve readability and simplify the
improvements that are coming in subsequent patches.

No functional change intended.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20220628135619.32410-12-imbrenda@linux.ibm.com
Message-Id: <20220628135619.32410-12-imbrenda@linux.ibm.com>
[frankja@linux.ibm.com: Dropped commit message line regarding review]
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>