drivers: dma: intel-adsp-gpdma: Account for LLPL wrapping

In case the LLP wraps we need to re-read the LLPU to make sure we return
the correct value.

Suggested-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>