gallium/util: Fix util_blitter_clear_depth_stencil() for num_layers>1
gallium/util: Fix util_blitter_clear_depth_stencil() for num_layers>1

Previously util_blitter_clear_depth_stencil() could not clear more
than the first layer. We need to generalise this as we did for
util_blitter_clear_render_target().

Signed-off-by: Edward O'Callaghan <117173807d5a49976a891944633465c0daea7f98@alterapraxis.com>
Signed-off-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler