drm/amdgpu: fix ucode out-of-bounds read warning

[ Upstream commit 8944acd0f9db33e17f387fdc75d33bb473d7936f ]

Clear warning that read ucode[] may out-of-bounds.

Signed-off-by: Tim Huang <Tim.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>