drm/amd/display: Fix typo in enable and disable symclk_se

[Why & How]
Symclk should be based on link_enc_inst, and symclk_fe_sel should be based
on stream_enc_inst.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Taimur Hassan <syed.hassan@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>