sky2: fix cleanup sequence in probe() function

The cleanup sequence in sky2_probe() that is called in case of an error is
mixed up in different places:

- pci_disable_device() is not called in each case the device has been enabled
before

- same for pci_disable_msi(): test_msi() may return with an error != EOPNOTSUPP
(due to failure of request_irq()). In that case msi is not disabled

- also failure of register_netdev() does not disable msi

This patch fixes the concerning parts.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>