staging: sep: add missing misc_deregister() on error in sep_register_driver_with_fs()

Add the missing misc_deregister() before return from
sep_register_driver_with_fs() in the error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>