Fix the following coccicheck warnings:

./fs/btrfs/volumes.c:1462:10-11: WARNING: return of 0/1 in function
'dev_extent_hole_check_zoned' with return type bool.
Reported-by: NAbaci Robot <abaci@linux.alibaba.com>
Signed-off-by: NJiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>