drm/amd/display: Skip pipe if the pipe idx not set properly

[why]
Driver crashes when pipe idx not set properly

[how]
Add code to skip the pipe that idx not set properly

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Muhammad Ahmed <ahmed.ahmed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>