net: wan: sdla: Fix cast from pointer to integer of different size

Since net_device.mem_start is unsigned long, it should not be cast to
int right before casting to pointer.  This fixes warning (compile
testing on alpha architecture):

    drivers/net/wan/sdla.c: In function ‘sdla_transmit’:
    drivers/net/wan/sdla.c:711:13: warning:
        cast to pointer from integer of different size [-Wint-to-pointer-cast]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wan/sdla.c

@@ -708,7 +708,7 @@ static netdev_tx_t sdla_transmit(struct sk_buff *skb,
 
 					spin_lock_irqsave(&sdla_lock, flags);
 					SDLA_WINDOW(dev, addr);
-					pbuf = (void *)(((int) dev->mem_start) + (addr & SDLA_ADDR_MASK));
+					pbuf = (void *)(dev->mem_start + (addr & SDLA_ADDR_MASK));
 					__sdla_write(dev, pbuf->buf_addr, skb->data, skb->len);
 					SDLA_WINDOW(dev, addr);
 					pbuf->opp_flag = 1;