ALSA: ppc: Remove i2c client removal hack

The i2c_driver.clients list is internal to I2C core and is going
to be removed.  No driver should access it. Unregister the
i2c client explicitly before deleting the i2c driver.

Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>