drm/i915: batch_obj vm offset must be u64

Otherwise it can overflow in 48-bit mode, and cause an incorrect
exec_start.

Before commit 5f19e2bf ("drm/i915: Merged
the many do_execbuf() parameters into a structure"), it was already an u64.
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Akash Goel <akash.goel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1686,7 +1686,7 @@ struct i915_execbuffer_params {
 	struct drm_file                 *file;
 	uint32_t                        dispatch_flags;
 	uint32_t                        args_batch_start_offset;
-	uint32_t                        batch_obj_vm_offset;
+	uint64_t                        batch_obj_vm_offset;
 	struct intel_engine_cs          *ring;
 	struct drm_i915_gem_object      *batch_obj;
 	struct intel_context            *ctx;