atm: eni: Add check for dma_map_single

[ Upstream commit 0f74b29a4f53627376cf5a5fb7b0b3fa748a0b2b ]

As the potential failure of the dma_map_single(),
it should be better to check it and return error
if fails.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>