Do not use memset to clean the whole struct kvm_s390_pv; instead,
explicitly clear the fields that need to be cleared.

Upcoming patches will introduce new fields in the struct kvm_s390_pv
that will not need to be cleared.
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20220628135619.32410-8-imbrenda@linux.ibm.com
Message-Id: <20220628135619.32410-8-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>