riscv: dts: sophgo: fix DMA data-width configuration for CV18xx

The "snps,data-width" property[1] defines the AXI data width of the DMA
controller as:

    width = 8 × (2^n) bits

(0 = 8 bits, 1 = 16 bits, 2 = 32 bits, ..., 6 = 512 bits)
where "n" is the value of "snps,data-width".

For the CV18xx DMA controller, the correct AXI data width is 32 bits,
corresponding to "snps,data-width = 2".

Test results on Milkv Duo S can be found here [2].

Link: https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/dma/snps%2Cdw-axi-dmac.yaml#L74 [1]
Link: https://gist.github.com/Sutter099/4fa99bb2d89e5af975983124704b3861

 [2]

Fixes: 514951a8 ("riscv: dts: sophgo: cv18xx: add DMA controller")
Co-developed-by: Yu Yuan <yu.yuan@sjtu.edu.cn>
Signed-off-by: Yu Yuan <yu.yuan@sjtu.edu.cn>
Signed-off-by: Ze Huang <huangze@whut.edu.cn>
Link: https://lore.kernel.org/r/20250428-duo-dma-config-v1-1-eb6ad836ca42@whut.edu.cn


Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Signed-off-by: Chen Wang <wangchen20@iscas.ac.cn>