IB/cma: use strlcpy() instead of strncpy()

gcc-8 reports

drivers/infiniband/core/cma_configfs.c: In function 'make_cma_dev':
./include/linux/string.h:245:9: warning: '__builtin_strncpy' specified
bound 64 equals destination size [-Wstringop-truncation]

We need to use strlcpy() to make sure the string is nul-terminated.

Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>