ALSA: ctxfi: Add fallback to default RSR for S/PDIF

ALSA: ctxfi: Add fallback to default RSR for S/PDIF

spdif_passthru_playback_get_resources() uses atc->pll_rate as the RSR
for the MSR calculation loop. However, pll_rate is only updated in
atc_pll_init() and not in hw_pll_init(), so it remains 0 after the
card init.

When spdif_passthru_playback_setup() skips atc_pll_init() for
32000 Hz, (rsr * desc.msr) always becomes 0, causing the loop to spin
indefinitely.

Add fallback to use atc->rsr when atc->pll_rate is 0. This reflects
the hardware state, since hw_card_init() already configures the PLL
to the default RSR.

Fixes: 8cc72361481f ("ALSA: SB X-Fi driver merge")
Cc: stable@vger.kernel.org
Signed-off-by: Harin Lee <me@harin.net>
Link: https://patch.msgid.link/20260406074913.217374-1-me@harin.net
Signed-off-by: Takashi Iwai <tiwai@suse.de>