xfs: fix xfs_error_get_cfg for negative errnos

xfs_error_get_cfg() is called with bp->b_error as an arg, which is
negative, so the switch statement won't ever find any matches.

This results in only the default error handler having any effect, as
EIO/ENOSPC/ENODEV get ignored due to the wrong sign.

It seems simplest to always flip the error sign to positive, so that
we can handle either negative errors in bp->b_error, or possibly a
positive errno via something like xfs_error_get_cfg(EIO) - this
future-proofs the function.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_sysfs.c

@@ -634,6 +634,9 @@ xfs_error_get_cfg(
 {
 	struct xfs_error_cfg	*cfg;
 
+	if (error < 0)
+		error = -error;
+
 	switch (error) {
 	case EIO:
 		cfg = &mp->m_error_cfg[error_class][XFS_ERR_EIO];