dmaengine: pch_dma: Replace pci_pool_alloc by pci_pool_zalloc

Inside pdc_alloc_desc(), pci_pool_alloc() followed by memset will be
replaced by pci_pool_zalloc()

Signed-off-by: Souptick joarder <jrdr.linux@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>