do_configure was using relative paths in do_configure with the assumption that
$S is the same as $B. This isn't always true, so explicitly use $S.
(From OE-Core rev: a01c103f54d2f588d78756d19f879eb82d0e5ae4)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>