UBUNTU:SAUCE: iio: common: st_sensors: fix channel data parsing

UBUNTU:SAUCE: iio: common: st_sensors: fix channel data parsing

BugLink: http://bugs.launchpad.net/bugs/1650189
Using realbits as i2c/spi read len, when that value is not byte aligned
(e.g 12 bits), lead to skip msb part of out data registers.
Fix this taking into account scan_type.shift in addition to
scan_type.realbits as read length:

read_len = DIV_ROUND_UP(realbits + shift, 8)

This fix has been tested on 8, 12, 16, 24 bit sensors

Fixes: e7385de5291e ("iio:st_sensors: align on storagebits boundaries")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
(backported from commit fd60b8949f4e85be2b9f364ab9c898c408664518)
(source: git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>