dmaengine: sh: make shdma_prep_dma_cyclic static

kbuild test robot reports that shdma_prep_dma_cyclic should be static, since
symbol is not declared, quick check revails that is the case

>> drivers/dma/sh/shdma-base.c:660:32: sparse: symbol 'shdma_prep_dma_cyclic'
>> was not declared. Should it be static?
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/sh/shdma-base.c

@@ -657,7 +657,7 @@ static struct dma_async_tx_descriptor *shdma_prep_slave_sg(
 			     direction, flags, false);
 }
 
-struct dma_async_tx_descriptor *shdma_prep_dma_cyclic(
+static struct dma_async_tx_descriptor *shdma_prep_dma_cyclic(
 	struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
 	size_t period_len, enum dma_transfer_direction direction,
 	unsigned long flags, void *context)