drm/dp: Fix comment in DP helper

Commit 4f71d0cb ("drm/dp: add a hw mutex around the transfer
functions. (v2)"), renamed the functions drm_dp_aux_register_i2c_bus()
and drm_dp_aux_unregister_i2c_bus() to drm_dp_aux_register() and
drm_dp_aux_unregister(), respectively. However, a comment referring to
the original names was not updated in the DP helper header file. Hence,
correct these names.
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_dp_helper.h

@@ -679,9 +679,9 @@ struct drm_dp_aux_msg {
  * An AUX channel can also be used to transport I2C messages to a sink. A
  * typical application of that is to access an EDID that's present in the
  * sink device. The .transfer() function can also be used to execute such
- * transactions. The drm_dp_aux_register_i2c_bus() function registers an
- * I2C adapter that can be passed to drm_probe_ddc(). Upon removal, drivers
- * should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter.
+ * transactions. The drm_dp_aux_register() function registers an I2C
+ * adapter that can be passed to drm_probe_ddc(). Upon removal, drivers
+ * should call drm_dp_aux_unregister() to remove the I2C adapter.
  * The I2C adapter uses long transfers by default; if a partial response is
  * received, the adapter will drop down to the size given by the partial
  * response for this transaction only.