drm/amdgpu: Fix FRU data checking

Ensure that when we memcpy, we don't end up copying more data than
the struct supports. For now, this is 16 characters for product number
and serial number, and 32 chars for product name

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>