util/ra: fix memory leak

CID: 1415909
Fixes: 7a34a0e890 "ra: Add a callback for selecting a register
                             from what's available."
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/util/register_allocate.c

@@ -672,6 +672,8 @@ ra_select(struct ra_graph *g)
          start_search_reg = r + 1;
    }
 
+   free(select_regs);
+
    return true;
 }