ALSA: firewire-lib: Avoid division by zero in apply_constraint_to_size()

ALSA: firewire-lib: Avoid division by zero in apply_constraint_to_size()

The step variable is initialized to zero. It is changed in the loop,
but if it's not changed it will remain zero. Add a variable check
before the division.

The observed behavior was introduced by commit 826b5de90c0b
("ALSA: firewire-lib: fix insufficient PCM rule for period/buffer size"),
and it is difficult to show that any of the interval parameters will
satisfy the snd_interval_test() condition with data from the
amdtp_rate_table[] table.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 826b5de90c0b ("ALSA: firewire-lib: fix insufficient PCM rule for period/buffer size")
Signed-off-by: Andrey Shumilin <shum.sdl@nppct.ru>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://patch.msgid.link/20241018060018.1189537-1-shum.sdl@nppct.ru
Signed-off-by: Takashi Iwai <tiwai@suse.de>