Btrfs: Show discard option in /proc/mounts

Christoph's patch e244a0aeb6a599c19a7c802cda6e2d67c847b154 doesn't display
the discard option in /proc/mounts, leading to some confusion for me.
Here's the missing bit.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1 file changed