drm/amd/display: change global buffer to local buffer

drm/amd/display: change global buffer to local buffer

[ Upstream commit 8ae5b155928c9183c2f37b5c4eec21037d958699 ]

[Why]
Multi-adapter calculate regamma table at the same time.
Two thread used the same global variable cause race
condition.

[How]
Change global buffer to local buffer

Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>