util: Rename variable in virStorageFileMetadataNew
util: Rename variable in virStorageFileMetadataNew

To prepare for subsequent change to use VIR_AUTOPTR logic rename
the @ret to @def.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>
Reviewed-by: Erik Skultety <2c14d38fa47c8799f1b9c16280abe27f8edfec6e@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

jfehlig/libvirt,eskultety/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,libvirt/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,eskultety/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,nertpinx/libvirt,jfehlig/libvirt,eskultety/libvirt,jfehlig/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,olafhering/libvirt,nertpinx/libvirt,eskultety/libvirt,andreabolognani/libvirt,zippy2/libvirt,jardasgit/libvirt,jardasgit/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,eskultety/libvirt,crobinso/libvirt,andreabolognani/libvirt