Btrfs: unlock everything properly in the error case for nocow

I was getting hung on umount when a transaction was aborted because a range
of one of the free space inodes was still locked.  This is because the nocow
stuff doesn't unlock anything on error.  This fixed the problem and I
verified that is what was happening.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>