b53: allow ports with higher numbers than CPU port

Our code was assuming CPU port uses the highest number. My BCM53573
device has eth0 connected to port 8 and eth1 connected to port 5. While
working on support for it I tried to:
1) Enable all ports (including port 8)
2) Set CPU port to 5

I noticed port 8 is not accessible anymore. It was just a development
process but it seems like something worth fixing anyway.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Jonas Gorski <jonas.gorski@gmail.com>

target/linux/generic/files/drivers/net/phy/b53/b53_common.c

@@ -1370,9 +1370,8 @@ static int b53_switch_init(struct b53_device *dev)
 			sw_dev->cpu_port = 5;
 	}
 
-	/* cpu port is always last */
-	sw_dev->ports = sw_dev->cpu_port + 1;
 	dev->enabled_ports |= BIT(sw_dev->cpu_port);
+	sw_dev->ports = fls(dev->enabled_ports);
 
 	dev->ports = devm_kzalloc(dev->dev,
 				  sizeof(struct b53_port) * sw_dev->ports,