Merge pull request #2994 from shenki/buildroot-2019.05.1

buildroot: Move to 2019.05.1 stable release
diff --git a/buildroot b/buildroot
index 0d430a2..645b4bc 160000
--- a/buildroot
+++ b/buildroot
@@ -1 +1 @@
-Subproject commit 0d430a2acbdac1c7b69d8af5de2fb21f7f25213d
+Subproject commit 645b4bc6047826e2c2f209641e688ee149cf03cb