KVM: s390: Improve determination of sizes in kvm_s390_import_bp_data()

* A multiplication for the size determination of a memory allocation
  indicated that an array data structure should be processed.
  Thus reuse the corresponding function "kmalloc_array".

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>

  This issue was detected also by using the Coccinelle software.

* Replace the specification of data structures by pointer dereferences
  to make the corresponding size determination a bit safer according to
  the Linux coding style convention.

* Delete the local variable "size" which became unnecessary with
  this refactoring.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Message-Id: <c3323f6b-4af2-0bfb-9399-e529952e378e@users.sourceforge.net>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>