ixgbe: fix namespace issue with ixgbe_dcb_txq_to_tc

We didn't need the prototype and it was causing namespace complaints so
I made it static.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index c2e09b9..34fdda2 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/drivers/net/ixgbe/ixgbe_main.c
@@ -648,7 +648,7 @@
  *
  * Returns : a tc index for use in range 0-7, or 0-3
  */
-u8 ixgbe_dcb_txq_to_tc(struct ixgbe_adapter *adapter, u8 reg_idx)
+static u8 ixgbe_dcb_txq_to_tc(struct ixgbe_adapter *adapter, u8 reg_idx)
 {
 	int tc = -1;
 	int dcb_i = adapter->ring_feature[RING_F_DCB].indices;