Fix threshold parsing logic of CPU sensors

This commit fixes threshold parsing logic of CPU sensors to make
a sensor can be registered even in case there is no threshold
setting.

Change-Id: I95641fb37472b65e8bf70925605b41c66bdad60f
Signed-off-by: Yoo, Jae Hyun <jae.hyun.yoo@intel.com>
diff --git a/sensors/src/Thresholds.cpp b/sensors/src/Thresholds.cpp
index b792a9b..c40d35d 100644
--- a/sensors/src/Thresholds.cpp
+++ b/sensors/src/Thresholds.cpp
@@ -253,7 +253,7 @@
 
 bool ParseThresholdsFromAttr(
     std::vector<thresholds::Threshold> &threshold_vector,
-    const std::string &input_path, const double scale_factor)
+    const std::string &input_path, const double &scale_factor)
 {
     for (auto &type : ATTR_TYPES)
     {