Factor out getPowerState() helper function

This same pattern had been open-coded in many of the sensor daemons;
let's reduce the duplication a bit.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Change-Id: I8556af30fdcd53cdf06e5a4911f9152d3265c7af
diff --git a/src/FanMain.cpp b/src/FanMain.cpp
index ff0ffaa..c55757c 100644
--- a/src/FanMain.cpp
+++ b/src/FanMain.cpp
@@ -405,17 +405,7 @@
                 redundancy = &systemRedundancy;
             }
 
-            PowerState powerState = PowerState::on;
-            auto findPower = baseConfiguration->second.find("PowerState");
-            if (findPower != baseConfiguration->second.end())
-            {
-                const auto* ptrPower =
-                    std::get_if<std::string>(&(findPower->second));
-                if (ptrPower != nullptr)
-                {
-                    setReadState(*ptrPower, powerState);
-                }
-            }
+            PowerState powerState = getPowerState(baseConfiguration->second);
 
             constexpr double defaultMaxReading = 25000;
             constexpr double defaultMinReading = 0;