dmaengine: xilinx: xdma: statify xdma_prep_interleaved_dma

xdma_prep_interleaved_dma() was local to file but not declared static,
leading to warning:

drivers/dma/xilinx/xdma.c:729:1: warning: no previous prototype for 'xdma_prep_interleaved_dma' [-Wmissing-prototypes]
  729 | xdma_prep_interleaved_dma(struct dma_chan *chan
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20231222094001.731889-1-vkoul@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/xilinx/xdma.c

@@ -725,7 +725,7 @@ xdma_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t address,
  * @xt: DMA transfer template
  * @flags: tx flags
  */
-struct dma_async_tx_descriptor *
+static struct dma_async_tx_descriptor *
 xdma_prep_interleaved_dma(struct dma_chan *chan,
 			  struct dma_interleaved_template *xt,
 			  unsigned long flags)