mesa: avoid returning a value in a void function

Fixes: 1d1722e9 ("mesa: add EXT_dsa NamedProgram functions")
Cc: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit a6873a8d)