xfs: xfs_iozero can return positive errno

[ Upstream commit cddc1162 ]

It was missed when we converted everything in XFs to use negative error
numbers, so fix it now. Bug introduced in 3.17 by commit 2451337d ("xfs: global
error sign conversion"), and should go back to stable kernels.

Thanks to Brian Foster for noticing it.

cc: <stable@vger.kernel.org> # 3.17, 3.18, 3.19, 4.0
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

fs/xfs/xfs_file.c

@@ -127,7 +127,7 @@ xfs_iozero(
 		status = 0;
 	} while (count);
 
-	return (-status);
+	return status;
 }
 
 /*