i2c: Adapt debug macros for KERN_* constants

According to kerneljanitors todo list all printk calls (beginning
a new line) should have an according KERN_* constant.
Those are the changes to the debug macros in the i2c subsystem
to meet this requirement. Also changing no-debug statements
to raw printks again.

Signed-off-by: Frank Seidel <frank@f-seidel.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Wolfram Sang <w.sang@pengutronix.de>