ASoC: kirkwood-dma: fix use of virt_to_phys()

This is part of a patch found in Rabeeh Khoury's git tree for the
cubox.

You can not use virt_to_phys() on the address returned from
dma_alloc_coherent(); it may not be part of the kernel direct-mapped
memory.  Fix this to use the DMA address instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>