usb: gadget: s3c2410_udc: use platform ids instead

This also fixes the error path: If the second device fails to register
we never remove the first one.
This is compile-tested only. I don't see any difference between those
two. Maybe we should just use one name instead?

Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>