tools/libgnttab: Fix build following c/s 3d3feaa456

VERS_1.2 can't extend itself.  It should extend VERS_1.1

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/libs/gnttab/libxengnttab.map

@@ -35,4 +35,4 @@ VERS_1.2 {
 		xengnttab_dmabuf_exp_wait_released;
 		xengnttab_dmabuf_imp_to_refs;
 		xengnttab_dmabuf_imp_release;
-} VERS_1.2;
+} VERS_1.1;