coccinelle: fix typo in comment

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/coccinelle/return_directly.cocci

@@ -1,4 +1,4 @@
-// replace 'R = X; return R;' with 'return R;'
+// replace 'R = X; return R;' with 'return X;'
 @@
 identifier VAR;
 expression E;