buildroot

grub: bump to 0.97-67

Bump to a more recent version of the Debian patches for grub legacy,
that fix an incorrect build with gcc 4.6.

Fixes #6092 and #2629.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>