driver: sensor: ina23x: driver lacks critical rshunt value resolution when set in milliohms.

[bperseghetti]

Describe the bug The INA23x driver does not allow setting of a rshunt value less than 1mOhm.

To Reproduce

1. Try to set the rshunt-milliohms to <0.5> in an overlay for MIMXRT1062_FMURT6 board ex:

   &lpi2c1 {
   status = "okay";
   pinctrl-0 = <&pinmux_lpi2c1>;
   pinctrl-names = "default";
   clock-frequency = <I2C_BITRATE_FAST>;
   
   ina230: ina230@41 {
       compatible = "ti,ina230";
       reg = <0x41>;
       config = <INA230_CONFIG(INA230_OPER_MODE_SHUNT_BUS_VOLTAGE_CONT,
                               INA230_CONV_TIME_2116, 
                               INA230_CONV_TIME_2116, 
                               INA230_AVG_MODE_64)>;
       current-lsb-microamps = <5000>;
       rshunt-milliohms = <0.5>;
   };
   };

2. Fails to compile as it is not an integer and milliohms does not have enough resolution.

Expected behavior Should allow setting value below 1 mOhm

Impact The driver eliminates the ability to use many standard VMU/FMU modules that range in 100-500 uOhm range. The lack of resolution on the rshunt Ohm value also eliminates the ability to "tune" to a resistors variance when using the TI documents example of 1mOhm.

[henrikbrixandersen]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.md

[bperseghetti]

Updated it, thanks.