i2c: Fix i2c speed command

i2c: Fix i2c speed command

This corrects i2c core to interpret the value returned by
i2c_set_bus_speed as a success indicator rather than the
actual speed that was set. When i2c_set_bus_speed returns
a failure code, the speed is unknown so the adapter speed
is set to zero.

Signed-off-by: Darwin Rambo <drambo@broadcom.com>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Reviewed-by: Steve Rae <srae@broadcom.com>
Acked-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>