drm/amd/display: Fix potential NULL and mem leak in create_links

Found by smatch:
drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:148 create_links()
error: potential null dereference 'link->link_enc'.  (kzalloc returns
null)

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>