btrfs: abort transaction in the process_one_buffer() log tree walk callback

In the process_one_buffer() log tree walk callback we return errors to the
log tree walk caller and then the caller aborts the transaction, if we
have one, or turns the fs into error state if we don't have one. While
this reduces code it makes it harder to figure out where exactly an error
came from. So add the transaction aborts after every failure inside the
process_one_buffer() callback, so that it helps figuring out why failures
happen.

Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>