drm/i915/gvt: Fix function comment doc errors

Caught by W=1 to fix left wrong function comment doc.

Reviewed-by: Hang Yuan <hang.yuan@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/handlers.c

@@ -3405,6 +3405,7 @@ bool intel_gvt_in_force_nonpriv_whitelist(struct intel_gvt *gvt,
  * @offset: register offset
  * @pdata: data buffer
  * @bytes: data length
+ * @is_read: read or write
  *
  * Returns:
  * Zero on success, negative error code if failed.