drm/i915: Update comment that sets I915_MODE_FLAG_INHERITED

The code was moved, but the comment not updated. It confused me.

Fixes: 7f4c6284 ("drm/i915: Assign hwmode after encoder state readout")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161219082423.27798-6-daniel.vetter@ffwll.ch