drivers: sensor: ina23x: calculate cal at compile.

Calculate the calibration value at compile for ina23x.
Maximizes the precision of the calcualtion value by
using 64bit math at compile, allows for removal
of rshunt config option.

Code cleaned up with clang-format.

Co-authored-by: Trent Piepho <tpiepho@gmail.com>
Signed-off-by: Benjamin Perseghetti <bperseghetti@rudislabs.com>