seabios: update submodule to 1.16.3 release

git shortlog 1e1da7a96300..rel-1.16.3
-------------------------------------

Gerd Hoffmann (1):
      limit address space used for pci devices.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

seabios @ a6ed6b70

-Subproject commit 1e1da7a963007d03a4e0e9a9e0ff17990bb1608d
+Subproject commit a6ed6b701f0a57db0569ab98b0661c12a6ec3ff8