net: usb: fix memory leak in smsc75xx_bind

Syzbot reported memory leak in smsc75xx_bind().
The problem was is non-freed memory in case of
errors after memory allocation.

backtrace:
  [<ffffffff84245b62>] kmalloc include/linux/slab.h:556 [inline]
  [<ffffffff84245b62>] kzalloc include/linux/slab.h:686 [inline]
  [<ffffffff84245b62>] smsc75xx_bind+0x7a/0x334 drivers/net/usb/smsc75xx.c:1460
  [<ffffffff82b5b2e6>] usbnet_probe+0x3b6/0xc30 drivers/net/usb/usbnet.c:1728

Fixes: d0cad871

 ("smsc75xx: SMSC LAN75xx USB gigabit ethernet adapter driver")
Cc: stable@kernel.vger.org
Reported-and-tested-by:  <syzbot+b558506ba8165425fee2@syzkaller.appspotmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>