AD HD-audio codec driver has a few code lines invoking
snd_get_num_conns() and using its return value as the array index
without checking.  This is basically safe in all those places; at the
second and later calls snd_get_num_conns() returns the value cached
from the first invocation, hence the value is always consistent.

However, it looks a bit confusing as if a lack of the proper check.
This patch introduces a new field num_smux_conns in ad198x_spec for
simplifying the code.  Now we store and refer to the value more
locally without invoking the extra function at each time.
Reported-by: Colin King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20200115100035.22511-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>