i965/gen7 renderbuffer: Set depth size based on LOD0 for 3D textures

If blorp is disabled for color clears, then piglit's
'gl-3.2-layered-rendering-clear-color-all-types 3d mipmapped'
will fail.

Currently, gen8 fails similarly on this test because gen8
does not use blorp.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>

src/mesa/drivers/dri/i965/gen7_wm_surface_state.c

@@ -489,7 +489,7 @@ gen7_update_renderbuffer_surface(struct brw_context *brw,
       depth *= 6;
       break;
    case GL_TEXTURE_3D:
-      depth = MAX2(rb->Depth, 1);
+      depth = MAX2(irb->mt->logical_depth0, 1);
       /* fallthrough */
    default:
       surftype = translate_tex_target(gl_target);