drm/ttm: Remove file_page_offset parameter from ttm_bo_device_init()

The parameter file_page_offset is a constant shared by all drivers. Just
replace it with the constant itself.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>