mtd: lpc32xx: use typedef for dma_filter_fn

Use existing typedef for dma_filter_fn to avoid duplicating type
definition.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240208202113.630190-1-krzysztof.kozlowski@linaro.org