ocfs2: Don't snprintf() without a format.

Some system files are per-slot.  Their names include the slot number.
ocfs2_sprintf_system_inode_name() uses the system inode definitions to
fill in the slot number with snprintf().

For global system files, there is no node number, and the name was
printed as a format with no arguments.  -Wformat-nonliteral and
-Wformat-security don't like this.  Instead, use a static "%s" format
and the name as the argument.

Signed-off-by: Joel Becker <joel.becker@oracle.com>