i2c-sibyte: Correct a comment about frequency

The frequency may have been once hardcoded to 100 kHz, but currently it is
passed as an argument to i2c_sibyte_add_bus(), so update the comment to
match code.  While at it, reformat a nearby comment for consistency.  No
functional changes.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>