i965/blorp/gen8: Stop multiplying depth by 6 for cubes
i965/blorp/gen8: Stop multiplying depth by 6 for cubes

intel_mipmap_tree::logical_depth0 is now in 2-D slices so there is no need
for us to multiply by 6 when we go to fill out a blorp surface state.

Signed-off-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler