ceph: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

This cleanup allows the return value of the functions to be made void,
as no logic should care if these files succeed or not.

Cc: "Yan, Zheng" <zyan@redhat.com>
Cc: Sage Weil <sage@redhat.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: ceph-devel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20190612145538.GA18772@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>