boost: fix the SRC_URI to point to an actual release, and not a master snapshot

boost: fix the SRC_URI to point to an actual release, and not a master snapshot

Sourceforge does a not-so-clever redirecting that fails miserably here:

     Proxy request sent, awaiting response... 301 Moved Permanently
     Location: http://downloads.sourceforge.net/project/boost/boost/snapshots/master/boost_1_62_0.tar.bz2 [following]

Also, boost developers are naming their snapshot tarballs the same as
release tarballs. The two things conspired together.

The new tarball does have the same checksum as the one in release
announcement, so we should be good now:

http://lists.boost.org/Archives/boost/2016/09/230886.php

Signed-off-by: Alexander Kanavin <alexander.kanavin@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>