btrfs: assign booleans to global reserve's full field

btrfs: assign booleans to global reserve's full field

We have a couple places that are assigning 0 and 1 to the full field of
the global reserve. This is harmless since 0 is converted to false and
1 converted to true, but for better readability, replace these with true
and false since the field is of type bool.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>