bonding: no need to print a message if debugfs_create_dir() fails

The debugfs core now will print a message if this function fails, so
don't duplicate that logic.  Also, no need to change the code logic if
the call fails either, as no debugfs calls should interrupt normal
kernel code for any reason.

Cc: Jay Vosburgh <j.vosburgh@gmail.com>
Cc: Veaceslav Falico <vfalico@gmail.com>
Cc: Andy Gospodarek <andy@greyhouse.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>