ASoC: SOF: ipc4-topology: Fix an unsigned comparison which can never be negative

ASoC: SOF: ipc4-topology: Fix an unsigned comparison which can never be negative

The return value from the call to sof_ipc4_get_valid_bits() is int.
However, the return value is being assigned to an unsigned
int variable 'out_ref_valid_bits', so making it an int.

Eliminate the following warning:
./sound/soc/sof/ipc4-topology.c:1537:6-24: WARNING: Unsigned expression compared with zero: out_ref_valid_bits < 0

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=4985
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20230516081116.71370-1-yang.lee@linux.alibaba.com
Signed-off-by: Mark Brown <broonie@kernel.org>