[ARM] 4728/1: BAST: Do not add IIS device on initialisation

The IIS device is being registered by the Simtec Audio
driver, and thus registering here causes an error due
to device tree naming collision.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>