buildroot: Update for kexec-lite changes

This picks up a change to kexec-lite to improve the kexec_file_load
error message.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/buildroot b/buildroot
index 3a4fc2a..522600d 160000
--- a/buildroot
+++ b/buildroot
@@ -1 +1 @@
-Subproject commit 3a4fc2a8881d1dfa6d6b6c57cafa0e4d620c1f5d
+Subproject commit 522600dd45a0200a420d3d28fe166e82f40594b5