i2c-sibyte: Remove the bus scan module parameter

The implementation is unsafe, and anyway one can achieve the same from
userspace using i2c-dev + i2cdetect.

Also tag i2c_sibyte_add_bus __init.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Ralf Baechle <ralf@linux-mips.org>