drm/amd/display: replace dio encoder access

[WHY]
replace dio encoder access to work with new dio encoder
assignment.

[HOW}
1. before validation, access dio encoder by get_temp_dio_link_enc()
2. after validation, access dio encoder through pipe_ctx->link_res

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Signed-off-by: Peichen Huang <PeiChen.Huang@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>