dmaengine: at_xdmac: fix un-exported functions

The at_xdmac_init_used_desc() and at_xdmac_prep_dma_memset()
functions are not exported outside the driver, so make them
static to avoid the following warnings:

drivers/dma/at_xdmac.c:459:6: warning: symbol 'at_xdmac_init_used_desc' was not declared. Should it be static?
drivers/dma/at_xdmac.c:1205:32: warning: symbol 'at_xdmac_prep_dma_memset' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/at_xdmac.c

@@ -456,7 +456,7 @@ static struct at_xdmac_desc *at_xdmac_alloc_desc(struct dma_chan *chan,
 	return desc;
 }
 
-void at_xdmac_init_used_desc(struct at_xdmac_desc *desc)
+static void at_xdmac_init_used_desc(struct at_xdmac_desc *desc)
 {
 	memset(&desc->lld, 0, sizeof(desc->lld));
 	INIT_LIST_HEAD(&desc->descs_list);
@@ -1202,7 +1202,7 @@ static struct at_xdmac_desc *at_xdmac_memset_create_desc(struct dma_chan *chan,
 	return desc;
 }
 
-struct dma_async_tx_descriptor *
+static struct dma_async_tx_descriptor *
 at_xdmac_prep_dma_memset(struct dma_chan *chan, dma_addr_t dest, int value,
 			 size_t len, unsigned long flags)
 {