I2C: fix 'ignore' module parameter handling

This patch fixes a bug in the handling of 'ignore' module parameters of I2C
client drivers.

Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>