drm/amd/display: Allow constructing DCE6 link encoder without DDC

When the DDC channel ID is set to CHANNEL_ID_UNKNOWN,
pass NULL to the AUX regs array.

This is necessary to support embedded connectors without DDC.

Fixes: 7c15fd8 ("drm/amd/display: dc/dce: add initial DCE6 support (v10)")
Link: https://gitlab.freedesktop.org/drm/amd/-/work_items/5192
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 38a70e5)

Author: Timur Kristóf

drivers/gpu/drm/amd/display/dc/resource/dce60/dce60_resource.c

@@ -753,7 +753,8 @@ static struct link_encoder *dce60_link_encoder_create(
 				     enc_init_data,
 				     &link_enc_feature,
 				     &link_enc_regs[link_regs_id],
-				     &link_enc_aux_regs[enc_init_data->channel - 1],
+				     enc_init_data->channel == CHANNEL_ID_UNKNOWN ?
+				     NULL : &link_enc_aux_regs[enc_init_data->channel - 1],
 				     enc_init_data->hpd_source >= ARRAY_SIZE(link_enc_hpd_regs) ?
 				     NULL : &link_enc_hpd_regs[enc_init_data->hpd_source]);
 	return &enc110->base;