dmaengine: mediatek: Use devm_platform_ioremap_resource() in mtk_uart_apdma_probe()

Simplify this function implementation by using a known wrapper function.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Link: https://lore.kernel.org/r/366e776c-8760-eeb7-c248-7380c9f4fd34@web.de
Signed-off-by: Vinod Koul <vkoul@kernel.org>