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

In the Linux kernel, the following vulnerability has been resolved:

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.