storage: Cleanup virStorageFileBackendGlusterReadlinkCallback
storage: Cleanup virStorageFileBackendGlusterReadlinkCallback

Rather than having two exit paths, let's use a @retval value
and VIR_STEAL_PTR in order to unite the exit path through the
error label.

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

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