orangefs: use correct string length

gcc-8 reports

fs/orangefs/dcache.c: In function 'orangefs_d_revalidate':
./include/linux/string.h:245:9: warning: '__builtin_strncpy' specified
bound 256 equals destination size [-Wstringop-truncation]

fs/orangefs/namei.c: In function 'orangefs_rename':
./include/linux/string.h:245:9: warning: '__builtin_strncpy' specified
bound 256 equals destination size [-Wstringop-truncation]

fs/orangefs/super.c: In function 'orangefs_mount':
./include/linux/string.h:245:9: warning: '__builtin_strncpy' specified
bound 256 equals destination size [-Wstringop-truncation]

We need one less byte or call strlcpy() to make it a nul-terminated
string.

Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>