[ATM]: [horizon] fix sparse warnings

Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NChas Williams <cmas@cmf.nrl.navy.mil>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/atm/horizon.c

@@ -1511,8 +1511,8 @@ static inline short setup_idle_tx_channel (hrz_dev * dev, hrz_vcc * vcc) {
     // a.k.a. prepare the channel and remember that we have done so.
     
     tx_ch_desc * tx_desc = &memmap->tx_descs[tx_channel];
-    u16 rd_ptr;
-    u16 wr_ptr;
+    u32 rd_ptr;
+    u32 wr_ptr;
     u16 channel = vcc->channel;
     
     unsigned long flags;