zink: type_main -> type_void_func

This type will be reused later on, so let's have the name describe what
is *is*, not what it's *used for*.

Cc: mesa-stable
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18244>
(cherry picked from commit 41dfed6e12)

.pick_status.json

@@ -10246,7 +10246,7 @@
         "description": "zink: type_main -> type_void_func",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c

@@ -4270,8 +4270,8 @@ nir_to_spirv(struct nir_shader *s, const struct zink_shader_info *sinfo, uint32_
    }
 
    SpvId type_void = spirv_builder_type_void(&ctx.builder);
-   SpvId type_main = spirv_builder_type_function(&ctx.builder, type_void,
-                                                 NULL, 0);
+   SpvId type_void_func = spirv_builder_type_function(&ctx.builder, type_void,
+                                                      NULL, 0);
    SpvId entry_point = spirv_builder_new_id(&ctx.builder);
    spirv_builder_emit_name(&ctx.builder, entry_point, "main");
 
@@ -4412,8 +4412,8 @@ nir_to_spirv(struct nir_shader *s, const struct zink_shader_info *sinfo, uint32_
                                    SpvExecutionModeXfb);
    }
    spirv_builder_function(&ctx.builder, entry_point, type_void,
-                                            SpvFunctionControlMaskNone,
-                                            type_main);
+                          SpvFunctionControlMaskNone,
+                          type_void_func);
 
    nir_function_impl *entry = nir_shader_get_entrypoint(s);
    nir_metadata_require(entry, nir_metadata_block_index);