ASoc: SOF: ipc4-pcm: fix uninit-value in sof_ipc4_pcm_dai_link_fixup_rate

Fix an issue detected by the Smatch tool:

sound/soc/sof/ipc4-pcm.c: sof_ipc4_pcm_dai_link_fixup_rate()
error: uninitialized symbol 'be_rate'.

The warning highlights a case where `be_rate` could remain uninitialized
if `num_input_formats` is zero, which would cause undefined behavior
when setting `rate->min` and `rate->max` based on `be_rate`.

To address this issue, a `WARN_ON_ONCE(!num_input_formats)` check was
added to ensure `num_input_formats` is greater than zero. If this
condition fails, the function returns `-EINVAL`, preventing the use of
an uninitialized `be_rate`.

This change improves the robustness of the function by catching an
invalid state early and providing better feedback during development.

Signed-off-by: Suraj Sonawane <surajsonawane0215@gmail.com>
Link: https://patch.msgid.link/20241107063609.11627-1-surajsonawane0215@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>