Update vboot submodule to upstream master

Updating from commit id 9c906110:
2019-08-06 06:07:01 +0000 - (vboot/tpm: fix return type inconsistencies)

to commit id a5afd01f:
2019-08-08 11:02:44 -0700 - (Minor fixes for clang)

This brings in 6 new commits.

Change-Id: Ic334ce8a5f24a0119fa2aaf000ce76c4c9e4932a
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34859
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>

1 files changed, 0 insertions, 0 deletions

diff --git a/3rdparty/vboot b/3rdparty/vboot
-Subproject 9c906110972f538ee5753845916ebd1f826f54b
+Subproject a5afd01feb0b4b45adbcd8ab38ab8a2ef2a2ef6