buildroot: Update powerpc-utils

This bumps the buildroot version to include the latest version of
powerpc-utils. It "has two nice update_flash fixes".

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/buildroot b/buildroot
index 25062c4..378a934 160000
--- a/buildroot
+++ b/buildroot
@@ -1 +1 @@
-Subproject commit 25062c4828517a568102aedaf0670c4c236ad53b
+Subproject commit 378a934e263c91ed41852818454c0d54e680658b