drm/amd/display: fix a crash when clock source is reference for non otg master pipe

drm/amd/display: fix a crash when clock source is reference for non otg master pipe

[why]
The function enumerates all pipes without checking pipe type. It is only
supposed to call program pixel clock for OTG master pipe only.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>