Add a module parameter to adjust I2C SCL clock period per board. This allows
some experimental fine tuning by end users to overcome quirky I2C device
problems.
Reported-by: "Aleksandr V. Piskunov" <aleksandr.v.piskunov@gmail.com> Signed-off-by: Andy Walls <awalls@radix.net> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>