drivers: sensor: ina23x: Use micro-ohms for rshunt

Changes rshunt-milliohms to rshunt-micro-ohms allowing for current
sensing of greater than 16.4A (1mOhm resistor). This is commonly
set to 100 uOhm for VMU/FMU boards/applications.

Co-authored-by: James Goppert <james.goppert@gmail.com>
Signed-off-by: Benjamin Perseghetti <bperseghetti@rudislabs.com>