iio: mxs-lradc: fix divider

iio: mxs-lradc: fix divider

commit 19bc4981a213d0c5b0e1e8b08815c0b26f01ec54 upstream.

All channels' single measurement are happening on CH 0. So enabling / disabling
the divider once is not enough, because it has impact on all channels.

Set only a flag, then check this on each measurement, and enable / disable the
divider as required.

Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>