davinci_cpdma: make cpdma_chan_split_pool static

The cpdma_chan_split_pool() function is not used outside of
the driver, so make it static to avoid the following sparse
warning:

drivers/net/ethernet/ti/davinci_cpdma.c:725:5: warning: symbol 'cpdma_chan_split_pool' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/davinci_cpdma.c

@@ -722,7 +722,7 @@ static void cpdma_chan_set_descs(struct cpdma_ctlr *ctlr,
  * cpdma_chan_split_pool - Splits ctrl pool between all channels.
  * Has to be called under ctlr lock
  */
-int cpdma_chan_split_pool(struct cpdma_ctlr *ctlr)
+static int cpdma_chan_split_pool(struct cpdma_ctlr *ctlr)
 {
 	int tx_per_ch_desc = 0, rx_per_ch_desc = 0;
 	int free_rx_num = 0, free_tx_num = 0;