hwmon: (max6639) Fix pulses-per-revolution implementation

hwmon: (max6639) Fix pulses-per-revolution implementation

The valid range for the pulses-per-revolution devicetree property is
1..4. The current code checks for a range of 1..5. Fix it.

Declare the variable used to retrieve pulses per revolution from
devicetree as u32 (unsigned) to match the of_property_read_u32() API.

The current code uses a postfix decrement when writing the pulses per
resolution into the chip. This has no effect since the value is evaluated
before it is decremented. Fix it by decrementing before evaluating the
value.

Fixes: 7506ebcd662b ("hwmon: (max6639) : Configure based on DT property")
Cc: Naresh Solanki <naresh.solanki@9elements.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>