The error code should be negative.  Since this ends up in the default case
anyway, this is harmless, but it's less confusing to negate it.  Also,
later patches will require a negative error code here.

Link: http://lkml.kernel.org/r/20170525103355.6760-1-jlayton@redhat.comSigned-off-by: NJeff Layton <jlayton@redhat.com>
Reviewed-by: NRoss Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Reviewed-by: NMatthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>