[PATCH] usbserial: Fixes leak in serial_open() error path.

If serial_open() fails at the port assignment or mutex_lock_interruptible()
is interrupted, the 'serial' object will never be freed.

We should call kref_put() when those errors happens.

Signed-off-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>