hwmon: (ibmpowernv) Use of_property_read_u32 at appropriate place

Simplify the code a bit and also improve readability.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Neelesh Gupta <neelegup@linux.vnet.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>