waf.bbclass: cd to ${S} before checking version

waf.bbclass: cd to ${S} before checking version

waf requires that the current working directory be the project root (in
this case ${S} when it is invoked. The check to get the waf version was
being executed as a prefunc for do_configure, which meant it was
executed before the current working directory was switched to ${S}, and
thus would fail with some recipes. Fix this by changing to ${S} before
executing "waf --version"

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
(cherry picked from commit aa168ee7f785ff007ca645db57698883922b5eb3)
Signed-off-by: Armin Kuster <akuster808@gmail.com>