renderer: fix layered depth clears.

fixes: gl-3.2-layered-rendering-clear-depth

src/vrend_renderer.c

@@ -1186,7 +1186,7 @@ void vrend_fb_bind_texture(struct vrend_resource *res,
 static void vrend_hw_set_zsurf_texture(struct vrend_context *ctx)
 {
    struct vrend_resource *tex;
-
+   int first_layer, last_layer;
    if (!ctx->sub->zsurf) {
       glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_STENCIL_ATTACHMENT,
                                 GL_TEXTURE_2D, 0, 0);
@@ -1197,7 +1197,11 @@ static void vrend_hw_set_zsurf_texture(struct vrend_context *ctx)
    if (!tex)
       return;
 
-   vrend_fb_bind_texture(tex, 0, ctx->sub->zsurf->val0, ctx->sub->zsurf->val1 & 0xffff);
+   first_layer = ctx->sub->zsurf->val1 & 0xffff;
+   last_layer = (ctx->sub->zsurf->val1 >> 16) & 0xffff;
+
+   vrend_fb_bind_texture(tex, 0, ctx->sub->zsurf->val0,
+			 first_layer != last_layer ? 0xffffffff : first_layer);
 }
 
 static void vrend_hw_set_color_surface(struct vrend_context *ctx, int index)