btrfs: simplify error detection flow during log replay

We have this fuzzy logic at btrfs_recover_log_trees() where we don't
abort the transaction and exit immediately after each function call that
returned an error, and instead have if-then-else logic or check if the
previous function call returned success before calling the next function.

Make the flow more straightforward by immediately aborting the transaction
and exiting after each function call failure. This also allows to avoid
two consecutive if statements that test the same conditions:

   if (!ret && wc.stage == LOG_WALK_REPLAY_ALL) {
        (...)
   }

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