usb/s3c-hsudc: fix error path

I doubt the clock is optional. In case it is it should not return with
an error code because we leak everything.

Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>