mmd_resolver: set 'src' arch for build repo solvables

Signed-off-by: Igor Gnatenko <ignatenko@redhat.com>

module_build_service/mmd_resolver.py

@@ -80,6 +80,7 @@ class MMDResolver(object):
 
         # Build-requires in case we are in build_repo.
         if repo == self.build_repo:
+            solvable.arch = "src"
             for deps in mmd.get_dependencies():
                 for name, streams in deps.get_buildrequires().items():
                     requires = None