drm/amdgpu: fix 64 bit divide in eeprom code

pos is 64 bits.

Fixes: c65b0805 ("drm/amdgpu: RAS EEPROM table is now in debugfs")
Cc: luben.tuikov@amd.com
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>