net: ethernet: ti: cpsw: Fix cpsw_add_ch_strings() printk format

When building on a 64-bit host we will get the following warning:

drivers/net/ethernet/ti/cpsw.c: In function 'cpsw_add_ch_strings':
drivers/net/ethernet/ti/cpsw.c:1284:19: warning: format '%d' expects
argument of type 'int', but argument 5 has type 'long unsigned int'
[-Wformat=]
     "%s DMA chan %d: %s", rx_dir ? "Rx" : "Tx",
                  ~^
                  %ld

Fix this by using an %ld format and casting to long.

Fixes: e05107e6

 ("net: ethernet: ti: cpsw: add multi queue support")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>