drm/radeon: Fix VRAM size calculation for VRAM >= 4GB

Add ULL prefix to avoid overflow.

Signed-off-by: Niels Ole Salscheider <niels_ole@salscheider-online.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
3 files changed