Make grub-mkconfig shut up about grep's stdout

debian/changelog

@@ -1,5 +1,10 @@
 grub2 (1.99-15) UNRELEASED; urgency=low
 
+  [ Adam Conrad ]
+  * grub.cfg_400.patch: Redirect grep stdout to /dev/null since
+    grub-mkconfig is "exec > grub.cfg.new", which causes grep's input
+    and output to be the same FD (LP: #934269) (closes: #652972)
+
   [ Colin Watson ]
   * no_libzfs.patch: Use xasprintf rather than asprintf.
   * Backport from upstream:

debian/patches/grub.cfg_400.patch

@@ -6,7 +6,7 @@ Index: b/util/grub-mkconfig.in
    esac
  done
  
-+if [ "x${grub_cfg}" != "x" ] && ! grep -q "^password " ${grub_cfg}.new ; then
++if [ "x${grub_cfg}" != "x" ] && ! grep "^password " ${grub_cfg}.new >/dev/null; then
 +  chmod 444 ${grub_cfg}.new || true
 +fi
 +