fix asset_user_access spec

Change-Id: I58957dc4609054936dbbff89e21602d87359e6e7
Reviewed-on: https://gerrit.instructure.com/42571
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Cody Cutrer <cody@instructure.com>