[libopencm3] Merge remote-tracking branch 'origin/master'

Submodule libopencm3 6246b33..5bc6bc4

diff --git a/libopencm3 b/libopencm3
index 6246b33231e683da93440ceb7d892d40fc7431c3..5bc6bc430a768a2e7392af4f4c93f306a0a654ba 160000 (submodule)
--- a/libopencm3
+++ b/libopencm3
@@ -1 +1 @@
-Subproject commit 6246b33231e683da93440ceb7d892d40fc7431c3
+Subproject commit 5bc6bc430a768a2e7392af4f4c93f306a0a654ba