chelsio: cxgb4: fix sparse warning

this patch fixes following sparse warning:

cxgb4_dcb.c:25:6: warning: symbol 'dcb_ver_array' was not declared. Should it be static?

Alongside making it const.
Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_dcb.c

@@ -22,7 +22,7 @@
 
 /* DCBx version control
  */
-char *dcb_ver_array[] = {
+static const char * const dcb_ver_array[] = {
 	"Unknown",
 	"DCBx-CIN",
 	"DCBx-CEE 1.01",