spirv: consider bitsize when handling OpSwitch cases

spirv: consider bitsize when handling OpSwitch cases

This reverts commit 7665383a33f9ce9256aa121cbe4d3bd948dff145 and is
squashed together with https://patchwork.freedesktop.org/patch/194610/
(spirv: avoid infinite loop / freeze in vtn_cfg_walk_blocks()) which
fixes https://bugs.freedesktop.org/show_bug.cgi?id=104359 properly.

Fixes: 9702fac68e (spirv: consider bitsize when handling OpSwitch cases)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104359
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>