PwmSensor: Fix function getValue returns wrong data type

Function "getValue" is defined as uint32_t but returns -1 in some cases.
Follow the function comment to change the return value from -1 to 0.

Change-Id: Ifd228c94e4ebe14d9bdea953506d17371f9e5f79
Signed-off-by: Yang Chen <yang.chen@quantatw.com>
diff --git a/src/PwmSensor.cpp b/src/PwmSensor.cpp
index a06d7c4..bffead9 100644
--- a/src/PwmSensor.cpp
+++ b/src/PwmSensor.cpp
@@ -212,12 +212,14 @@
     std::ifstream ref(sysPath);
     if (!ref.good())
     {
-        return -1;
+        std::cerr << "Error opening " << sysPath << "\n";
+        return 0;
     }
     std::string line;
     if (!std::getline(ref, line))
     {
-        return -1;
+        std::cerr << "Error reading pwm at " << sysPath << "\n";
+        return 0;
     }
     try
     {
@@ -226,7 +228,7 @@
     }
     catch (const std::invalid_argument&)
     {
-        std::cerr << "Error reading pwm at " << sysPath << "\n";
+        std::cerr << "Error converting pwm\n";
         // throw if not initial read to be caught by dbus bindings
         if (errThrow)
         {