In intel_draw_buffer, there exists a workaround to prevent
_mesa_update_framebuffer from creating a swrast depth wrapper when
using separate stencil. This commit fixes the workaround, which was
incomplete for s8z24 texture renderbuffers.
Fixes fbo-blit-d24s8 on gen5 with separate stencil manually enabled.
Signed-off-by: Chad Versace <chad@chad-versace.us>