Fix warning

drivers/i2c/chips/tlv320aic23.c: In function 'aic23_exit':
drivers/i2c/chips/tlv320aic23.c:671: warning: unused variable 'res'
Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Signed-off-by: Kevin Hilman <khilman@mvista.com>