i965: Drop redundant check for non-tiled depth buffer

i965: Drop redundant check for non-tiled depth buffer

Depth buffers are always Y-tiled. In brw_miptree_choose_tiling()
driver opts to use linear buffers for small and 1D but this does
not apply for depth - GL_DEPTH_COMPONENT and GL_DEPTH_STENCIL_EXT
are considered first.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>