ncpfs: fix error return code in ncp_parse_options()

Fix to return -EINVAL from the option parse error handling
case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>