v3dv: assert that our framebuffers are single sampled

This makes it easier to track CTS test fails related to multisampling,
which we don't support yet.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>

src/broadcom/vulkan/v3dv_cmd_buffer.c

@@ -1856,6 +1856,9 @@ cmd_buffer_emit_render_pass_rcl(struct v3dv_cmd_buffer *cmd_buffer)
       const struct v3dv_image *image = iview->image;
       const struct v3d_resource_slice *slice = &image->slices[iview->base_level];
 
+      /* FIXME */
+      assert(image->samples == VK_SAMPLE_COUNT_1_BIT);
+
       const uint32_t *clear_color =
          &state->attachments[attachment_idx].clear_value.color[0];