mdio_bus: NULL dereference on allocation error

If bus = kzalloc() fails then we end up dereferencing bus when we do
"bus->irq[i] = PHY_POLL;".  The code is a little simpler if we reverse
the NULL check and return directly on failure.

Fixes: e7f4dc35 ('mdio: Move allocation of interrupts into core')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/mdio_bus.c

@@ -102,11 +102,12 @@ struct mii_bus *mdiobus_alloc_size(size_t size)
 		alloc_size = sizeof(*bus);
 
 	bus = kzalloc(alloc_size, GFP_KERNEL);
-	if (bus) {
+	if (!bus)
+		return NULL;
+
 	bus->state = MDIOBUS_ALLOCATED;
 	if (size)
 		bus->priv = (void *)bus + aligned_size;
-	}
 
 	/* Initialise the interrupts to polling */
 	for (i = 0; i < PHY_MAX_ADDR; i++)