drm/amdgpu: fix integer overflow test in amdgpu_bo_list_create()

We accidentally left out the size of the amdgpu_bo_list struct.  It
could lead to memory corruption on 32 bit systems.  You'd have to
pick the absolute maximum and set "num_entries == 59652323" then size
would wrap to 16 bytes.

Fixes: 920990cb

 ("drm/amdgpu: allocate the bo_list array after the list")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Bas Nieuwenhuizen <basni@chromium.org>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>