i2c: busses: remove superfluous ignoring of children for RPM

These days, the I2C core ensures that the embedded adapter device
ignores the PM states of its children already. Because the adapter
device is an opaque logical device, there is no need for drivers to
repeat that again.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>