dmaengine: zynqmp: avoid cast warning

The newly added zynqmp_dma driver produces a warning on 32-bit architectures
when dma_addr_t is 64-bit wide:

drivers/dma/xilinx/zynqmp_dma.c: In function 'zynqmp_dma_config_sg_ll_desc':
drivers/dma/xilinx/zynqmp_dma.c:321:9: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
        ((dma_addr_t)sdesc - (dma_addr_t)chan->desc_pool_v);
         ^
drivers/dma/xilinx/zynqmp_dma.c:321:29: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
        ((dma_addr_t)sdesc - (dma_addr_t)chan->desc_pool_v);

This changes the cast to the more appropriate uintptr_t.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>