dmaengine: jz4740: disable/unprepare clk if probe fails

in error path of jz4740_dma_probe(), call clk_disable_unprepare() to clean
up.

Found by Linux Driver Verification project (linuxtesting.org).

Fixes: 25ce6c35 MIPS: jz4740: Remove custom DMA API
Signed-off-by: Tobias Jordan <Tobias.Jordan@elektrobit.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>