drm/amd/display: fix double memory allocation

[Why & How]
when trying to fix a nullptr dereference on VMs,
accidentally doubly allocated memory for the non VM
case. removed the extra link_srv creation since
dc_construct_ctx is called in both VM and non VM cases
Also added a proper fail check for if kzalloc fails

Cc: stable@vger.kernel.org
Cc: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Leo Ma <Hanghong.Ma@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Martin Leung <Martin.Leung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>