classes/gnomebase: set S using GNOMEBN instead of BPN

classes/gnomebase: set S using GNOMEBN instead of BPN

For the majority of recipes, the default S is correct. But a few recipes
have a package name that is not the recipe name (such as GConf), and
we already handle this in the SRC_URI assignment.

Use GNOMEBN in the S assignment instead of PN so that S is correct too.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>