etnaviv: fix segfault after compile failure

Do not try to determine the shader stage from the compiled shader
variant, which may be NULL after compile failure. Instead, get it
from the NIR shader.

Fixes a segfault when trying to evaluate etna_shader_stage(NULL)
after compile failure.

Suggested-by: Christian Gmeiner <cgmeiner@igalia.com>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Fixes: 3d49619071 ("etnaviv: add support for performance warnings")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24178>

src/gallium/drivers/etnaviv/etnaviv_shader.c

@@ -347,9 +347,9 @@ etna_shader_update_vs_inputs(struct compiled_shader_state *cs,
 }
 
 static inline const char *
-etna_shader_stage(struct etna_shader_variant *shader)
+etna_shader_stage(struct etna_shader *shader)
 {
-   switch (shader->stage) {
+   switch (shader->nir->info.stage) {
    case MESA_SHADER_VERTEX:     return "VERT";
    case MESA_SHADER_FRAGMENT:   return "FRAG";
    case MESA_SHADER_COMPUTE:    return "CL";
@@ -368,7 +368,7 @@ dump_shader_info(struct etna_shader_variant *v, struct util_debug_callback *debu
    util_debug_message(debug, SHADER_INFO,
          "%s shader: %u instructions, %u temps, "
          "%u immediates, %u loops",
-         etna_shader_stage(v),
+         etna_shader_stage(v->shader),
          v->code_size / 4,
          v->num_temps,
          v->uniforms.count,
@@ -445,7 +445,7 @@ etna_shader_variant(struct etna_shader *shader,
       perf_debug_message(debug, SHADER_INFO,
                          "%s shader: recompiling at draw time: global "
                          "0x%08x\n",
-                         etna_shader_stage(v), key->global);
+                         etna_shader_stage(shader), key->global);
    }
 
    return v;