UAS: fix alignment of scatter/gather segments

This is the UAS version of

747668dbc061b3e62bc1982767a3a1f9815fcf0e
usb-storage: Set virt_boundary_mask to avoid SG overflows

We are not as likely to be vulnerable as storage, as it is unlikelier that UAS is run over a controller without native support for SG, but the issue exists.
The issue has been existing since the inception of the driver.

Fixes 115bb1ffa54ac ("USB: Add UAS driver")