drm/amd/display: Use _free() macro for amdgpu_dm_update_connector_after_detect()

By using a _free() macro multiple duplicated snippets of code to free
the sink can be dropped. The sink will be released when leaving scope.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>