ALSA: au88x0: Fix assignment in if condition

PCI AU88x0 driver code contains a lot of assignments in if condition,
which is a bad coding style that may confuse readers and occasionally
lead to bugs.

This patch is merely for coding-style fixes.  A potential real fix is
about the PCI AGP bridge management refcount in addition while spotted
out during conversions.

Link: https://lore.kernel.org/r/20210608140540.17885-36-tiwai@suse.de


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