ALSA: seq: Fix leftovers at probe error path

The sequencer core module doesn't call some destructors in the error
path of the init code, which may leave some resources.

This patch mainly fix these leaks by calling the destructors
appropriately at alsa_seq_init().  Also the patch brings a few
cleanups along with it, namely:

- Expand the old "if ((err = xxx) < 0)" coding style
- Get rid of empty seq_queue_init() and its caller
- Change snd_seq_info_done() to void

Last but not least, a couple of functions lose __exit annotation since
they are called also in alsa_seq_init().

No functional changes but minor code cleanups.

Signed-off-by: Takashi Iwai <tiwai@suse.de>