radeonsi: code shuffling in si_init_depth_surface
radeonsi: code shuffling in si_init_depth_surface

use fewer local variables, re-order the assignments, so that the GFX9 diff
is smaller here.

Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler