dma: intel-adsp: hda: avoid division by 0

A division by 0 has once been observed inside
intel_adsp_hda_dma_host_reload(). It is apparently caused by a
preceding logic or hardware error, but in any case values, read from
the hardware should be checked for 0 before being used as a divisor.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>