r6040: rework init_one error handling

This patch reworks the error handling in r6040_init_one
in order not to leak resources and correcly unmap and release
PCI regions of the MAC. Also prefix printk's with the driver name
for clarity.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>