[PATCH] USB: sl811_cs needs platform_device conversion too

The switchover to "platform_driver" from "device_driver" missed
one rather essential usage, which broke the sl811_cs driver ...
this resolves the omission.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>