drm/xe/guc: Use the steering flag when printing registers

The printing code was doing a test on which list a register was in to
decide whether it is steered or not. That might be valid at this
moment but there may be other reasons for extended lists in the
future. Plus, there is a flag specifically for identifying steered
registers. So, just use that instead - it is simpler and safer.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20250417195215.3002210-3-John.C.Harrison@Intel.com