dmaengine: sun6i: fix build failure on x86, xilinx targets

Since the driver defined COMPILE_TEST, it gets compiled for different arch's
The driver uses __virt_to_phys() insteadof virt_to_phys, so replace it

drivers/dma/sun6i-dma.c: In function ‘sun6i_dma_dump_chan_regs’:
drivers/dma/sun6i-dma.c:203: error: implicit declaration of function '__virt_to_phys'

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>