sunxi-mail: hack to work around autobuilder issue

sunxi-mail: hack to work around autobuilder issue

Fixes http://autobuild.buildroot.org/results/5a5/5a50be9feeb5da7694e9a42f615f0b7276319aeb/

The recent change to use git submodules for sunxi-mali instead of the github
wrapper without changing the version unfortunately doesn't work for people
who have already built sunxi-mali, as the existing github tarball will be
used instead of buildroot doing a clean git clone (with submodules).

The sunxi-mali commit we are using is the latest in the repo, so we cannot
fix it by bumping the version.  Instead simply remove the last character of
the VERSION sha1 so the existing tarballs are no longer used.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>