drm/i915: Remove unwanted ghost obj check

vm_fault_ttm() should not expect ttm ghost obj so remove that check.

Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221024144558.27747-1-nirmoy.das@intel.com