drm/amdgpu: avoid reading vf2pf info size from FB

[ Upstream commit 3bcc0ee1 ]

VF can't access FB when host is doing mode1 reset. Using sizeof to get
vf2pf info size, instead of reading it from vf2pf header stored in FB.

Signed-off-by: Zhigang Luo <Zhigang.Luo@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>