virTypedParameterAssignValueVArgs: Ensure proper typed param type in caller

virTypedParameterAssignValueVArgs: Ensure proper typed param type in caller

There are two callers of virTypedParameterAssignValueVArgs.

- 'virTypedParameterAssignValue' always uses the correct type, thus
  doesn't need to be modified. Just use the proper type in the function
  declaration

- 'virTypedParameterAssign' can get improper type, but we can move the
  validation into it decreasing the scope in which failures need to be
  propagated.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>