ALSA: sb: Fix assignment in if condition

ALSA: sb: Fix assignment in if condition

A lot of code for SB drivers is in a legacy style with assignment in
if condition.  This also made harder to catch some bugs (e.g. the
commit 1c98f574403d "ALSA: emu8000: Fix a use after free in
snd_emu8000_create_mixer").

This patch fixes the coding style.  All are rather simple conversions
and there should be no functional changes.
(The changes in snd_emu8000_new() for hw->res_port1, 2 and 3 are
 slightly different from the older ones, but this shouldn't matter
 much in practice.)

Link: https://lore.kernel.org/r/20210608140540.17885-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>