dma: omap: check dma channel data_type

When setting dma channel 'data_type', if (value & 3) == 3,
the set 'data_type' is said to be bad. This also leads to an
OOB access in 'omap_dma_transfer_generic', while doing
cpu_physical_memory_r/w operations. Add check to avoid it.

Reported-by: Jiang Xin <jiangxin1@huawei.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-id: 20170127120528.30959-1-ppandit@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>