[PATCH] ld: add missing period after @xref

[Jan Beulich]

At least older versions of one of the doc generation tools complain
(warn) about it missing.

--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -7244,7 +7244,7 @@ Currently there is only one plugin shipp
 be added here later.
 
 Plugins are enabled via the use of the @option{-plugin @var{name}}
-command line option. @xref{Options}
+command line option. @xref{Options}.
 
 @menu
 * libdep Plugin::	Static Library Dependencies Plugin