glsl: Fix gl_shader_stage enum unsigned comparison

Replace -1 with MESA_SHADER_NONE enum value to fix sign related warning:

external/mesa3d/src/compiler/glsl/link_varyings.cpp:1415:25: warning: comparison of constant -1 with expression of type 'gl_shader_stage' is always true [-Wtautological-constant-out-of-range-compare]
        (consumer_stage != -1 && consumer_stage != MESA_SHADER_FRAGMENT))) {
         ~~~~~~~~~~~~~~ ^  ~~

Reviewed-by: Nicolai Hähnle <[email protected]>
Signed-off-by: Rob Herring <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mesa/state_tracker/st_context.h b/src/mesa/state_tracker/st_context.h
index 631c3aee0ac..6dcf13352b9 100644
--- a/src/mesa/state_tracker/st_context.h
+++ b/src/mesa/state_tracker/st_context.h
@@ -363,6 +363,8 @@ st_shader_stage_to_ptarget(gl_shader_stage stage)
       return PIPE_SHADER_TESS_EVAL;
    case MESA_SHADER_COMPUTE:
       return PIPE_SHADER_COMPUTE;
+   default:
+      break;
    }
 
    assert(!"should not be reached");