The underlying device support will set the device dma_mask pointer
if DMA is set up properly for the device.  Remove the check for and
assignment of dma_mask when it is null. Instead, just error out if
the dma_set_mask_and_coherent function fails because dma_mask is null.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>