power: Explicitly select pmic device's bus

The current pmic i2c code assumes the current i2c bus is
the same as the pmic device's bus. There is nothing ensuring
that to be true. Therefore, select the proper bus before performing
a transaction.

Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>