drivers/net/wan/pc300_drv: fix bug caught by gcc warning

The warning

drivers/net/wan/pc300_drv.c: In function ‘cpc_open’:
drivers/net/wan/pc300_drv.c:2942: warning: ‘br’ may be used
uninitialized in this function

was valid.  Ensure 'br' is initialized in all cases.
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/net/wan/pc300_drv.c

@@ -2833,6 +2833,8 @@ static int clock_rate_calc(uclong rate, uclong clock, int *br_io)
 	int br, tc;
 	int br_pwr, error;
 
+	*br_io = 0;
+
 	if (rate == 0)
 		return (0);