conf: Export virDomainDiskSourceFormat

Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/libvirt_private.syms

@@ -354,6 +354,7 @@ virDomainDiskSetDriver;
 virDomainDiskSetFormat;
 virDomainDiskSetSource;
 virDomainDiskSetType;
+virDomainDiskSourceFormat;
 virDomainDiskTranslateSourcePool;
 virDomainFeatureTypeFromString;
 virDomainFeatureTypeToString;