dmaengine: xilinx: vdma: icg should be difference of stride and hsize

This patch modifies the icg field to match the description
as mentioned in the DMA Linux framework.

Signed-off-by: Srikanth Thokala <sthokal@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>