ASoC: rt5640: Handle 0Hz sysclk during stream shutdown

ASoC: rt5640: Handle 0Hz sysclk during stream shutdown

Commit 2458adb8f92a ("SoC: simple-card-utils: set 0Hz to sysclk when
shutdown") sends a 0Hz sysclk request during stream shutdown to clear
codec rate constraints. The rt5640 codec forwards this 0Hz to
clk_set_rate(), which can cause clock controller firmware faults on
platforms where MCLK is SoC-driven (e.g. Tegra) and 0Hz falls below
the hardware minimum rate.

Handle the 0Hz case by clearing the internal sysclk state and
returning early, avoiding the invalid clk_set_rate() call.

Signed-off-by: Sheetal <sheetal@nvidia.com>
Link: https://patch.msgid.link/20260406090547.988966-1-sheetal@nvidia.com
Signed-off-by: Mark Brown <broonie@kernel.org>