btrfs: fix clashing number of the enhanced balance usage filter

btrfs: fix clashing number of the enhanced balance usage filter

I've accidentally picked an already used number for the enhanced usage
filter represented by BTRFS_BALANCE_ARGS_USAGE_RANGE, clashing with
BTRFS_BALANCE_ARGS_CONVERT. Introduced during the development phase,
no backward compatibility issues.

Reported-by: Holger Hoffstätte <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Fixes: bc3094673f22 ("btrfs: extend balance filter usage to take minimum and maximum")
Signed-off-by: David Sterba <[email protected]>
Signed-off-by: Chris Mason <[email protected]>