panfrost: do not double-insert shader into hash-table

We were inserting twice here, once without holding the lock before
compiling the shaders, and once after while holding it. Let's remove
the insert without the lock.

Fixes: ae3fb3089f ("panfrost: Add infrastructure for internal AFBC compute shaders")
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35336>

src/gallium/drivers/panfrost/pan_mod_conv_cso.c

@@ -467,7 +467,6 @@ panfrost_get_mod_convert_shaders(struct panfrost_context *ctx,
 
    shader = rzalloc(ctx->mod_convert_shaders.shaders, struct pan_mod_convert_shader_data);
    shader->key = key;
-   _mesa_hash_table_insert(ctx->mod_convert_shaders.shaders, &shader->key, shader);
 
 #define COMPILE_SHADER(name, ...)                                              \
    {                                                                           \