dmaengine: mediatek: simplify the return expression of mtk_uart_apdma_runtime_resume()

Simplify the return expression.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Link: https://lore.kernel.org/r/20200915032622.1772309-1-liushixin2@huawei.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>