i2c: Do not use device name after device_unregister

dev_dbg outputs dev_name, which is released with device_unregister. This bug
resulted in output like this:

i2c Xy2�0: adapter [SMBus I801 adapter at 1880] unregistered

The right output would be:
i2c i2c-0: adapter [SMBus I801 adapter at 1880] unregistered

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>