drivers/atm/ambassador: kill uninit'd var warning, and fix bug

An uninitialized variable warning illuminated an area where indeed the
variable was being used without initialization.  Unfortunately, after
verifying all such paths were fixed, the warning still appears.  So we
follow the initialization practice of other variables in this function.
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/atm/ambassador.c

@@ -1040,7 +1040,7 @@ static int amb_open (struct atm_vcc * atm_vcc)
   struct atm_qos * qos;
   struct atm_trafprm * txtp;
   struct atm_trafprm * rxtp;
-  u16 tx_rate_bits;
+  u16 tx_rate_bits = -1; // hush gcc
   u16 tx_vc_bits = -1; // hush gcc
   u16 tx_frame_bits = -1; // hush gcc
   
@@ -1096,6 +1096,8 @@ static int amb_open (struct atm_vcc * atm_vcc)
 	    r = round_up;
 	  }
 	  error = make_rate (pcr, r, &tx_rate_bits, NULL);
+	  if (error)
+	    return error;
 	  tx_vc_bits = TX_UBR_CAPPED;
 	  tx_frame_bits = TX_FRAME_CAPPED;
 	}