i2c-powermac: Drop temporary name buffer

We no longer need to write the adapter name to a temporary buffer.
We can write it directly to the i2c_adapter's name field. This is
more efficient.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Michel Daenzer <michel@daenzer.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>