Fix bad generated path for generated sources

Fix bad generated path for generated sources

The yang-maven-plugin appears to generate code into
target/generated-sources/sal and target/generated-sources/config, and
not (anymore?) into src/main/yang-gen-sal & src/main/yang-gen-config.

Without making this change, there is a lot of red in Eclipse at least,
because generate code is not seen on the classpath.

I wonder in fact how this could ever have even worked in CLI mvn build,
or other IDEs.

Change-Id: Ib2c67bd7b52f1e038626161d29886457c3db8566
Signed-off-by: Michael Vorburger <vorburger@redhat.com>