net: macb: add missing free_netdev() on error in macb_probe()

Add the missing free_netdev() before return from function macb_probe()
in the platform_get_irq() error handling case.

Fixes: c69618b3

 ("net/macb: fix probe sequence to setup clocks earlier")
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>