bcache: reduce redundant code in bch_cached_dev_run()

bcache: reduce redundant code in bch_cached_dev_run()

In bch_cached_dev_run(), free(env[1])|free(env[2])|free(buf)
show up three times. This patch introduce out tag in
which free(env[1])|free(env[2])|free(buf) are only called
one time. If we need to call free() when errors occur,
we can set error code to ret, and then goto out tag directly.

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20210411134316.80274-2-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>