[ARM] 5246/1: tosa: add proper clock alias for tc6393xb clock

Add clock alias for clock that is used by tc6393xb device on tosa.
As that chip plays pretty major part in tosa life and is currently
disabled, this is 2.4.27 material.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>