pkgconfig: update SRC_URI

The git repo for pkg-config was changed, so update the
SRC_URI accordingly with the new link.

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 9fd1b9b8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>