dt-bindings: ufs: ti: Add missing 'additionalProperties: false'

The ti,j721e-ufs schema is missing an 'additionalProperties: false'. Add
that and and the missing assigned-clock properties.

Acked-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Rob Herring <robh@kernel.org>