ALSA: seq: Treat snd_seq_client object directly in client drivers

Introduce the new helpers, snd_seq_kernel_client_get() and _put() for
kernel client drivers to treat the snd_seq_client more directly.
This allows us to reduce the exported symbols and APIs at each time we
need to access some field in future.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-20-tiwai@suse.de


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