build: fix typo in error message

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Fixes: f62bbee55d

scripts/git-submodule.sh

@@ -28,7 +28,7 @@ error() {
     echo
     echo "and then manually update submodules prior to running make, with:"
     echo
-    echo " $ scripts/git-sbumodule.sh update $modules"
+    echo " $ scripts/git-submodule.sh update $modules"
     echo
     exit 1
 }