drm/i915/cnl: Fix comment about AUX IO power well enable/disable

The comments match an earlier version of the patch, fix them to match
the current state.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1498750622-14023-6-git-send-email-imre.deak@intel.com