bcache: fix return value error in bch_journal_read()

When everything is OK in bch_journal_read(), finally the return value
is returned by,
	return ret;
which assumes ret will be 0 here. This assumption is wrong when all
journal buckets as are full and filled with valid journal entries. In
such cache the last location referencess read_bucket() sets 'ret' to
1, which means new jset added into jset list. The jset list is list
'journal' in caller run_cache_set().

Return 1 to run_cache_set() means something wrong and the cache set
won't start, but indeed everything is OK.

This patch changes the line at end of bch_journal_read() to directly
return 0 since everything if verything is good. Then a bogus error
is fixed.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>