drm/i915/dp: Don't WARN on failed link-retrain modeset

drm/i915/dp: Don't WARN on failed link-retrain modeset

After a bad link state is detected, the sink capabilities with which the
link was originally trained could have changed: for instance another
sink got connected or the retraining was forced after the rate/lane count
got decreased (as a fallback). In these cases the retraining modeset
fails as expected also printing a debug message, so don't WARN on it.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240712135724.660399-3-imre.deak@intel.com