Undefined variable $display in panels_ipe.api.php

Although not a real bug, it is worth to fix it. In panels_ipe.api.php the hook_panels_ipe_access() example uses the variable $display but the passed in variable is named $panels_display. I think the passed in variable should be $display of class panels_display to be consistent with the rest of the code.

Please review the attached one-liner patch.