NFS: Fix potential buffer overflowin nfs_sysfs_link_rpc_client()

In the Linux kernel, the following vulnerability has been resolved: NFS: Fix potential buffer overflowin nfs_sysfs_link_rpc_client() name is char[64] where the size of clnt->cl_program->name remains unknown. Invoking strcat() directly will also lead to potential buffer overflow. Change them to strscpy() and strncat() to fix potential issues.