Handle file errors when device path gets unbound

occ-control was asserting when the hwmon path would get removed due to
device being unbound. This change will gracefully handle the path
getting removed / added back.

Tested on Raininer by unbind/bind of devices:
  echo occ-hwmon.2 > /sys/bus/platform/drivers/occ-hwmon/unbind
  echo occ-hwmon.2 > /sys/bus/platform/drivers/occ-hwmon/bind

Change-Id: I46fd2c2c54868ffb8183d3dc49cd0c2751165d3b
Signed-off-by: Chris Cain <cjcain@us.ibm.com>
diff --git a/occ_status.hpp b/occ_status.hpp
index 6a00676..6376b6c 100644
--- a/occ_status.hpp
+++ b/occ_status.hpp
@@ -204,7 +204,7 @@
      *
      *  @return path or empty path if not found
      */
-    fs::path getHwmonPath() const;
+    fs::path getHwmonPath();
 
   private:
     /** @brief OCC dbus object path */
@@ -251,6 +251,9 @@
     sdeventplus::Event sdpEvent;
 #endif
 
+    /** @brief hwmon path for this OCC */
+    fs::path hwmonPath;
+
     /** @brief Callback function on host control signals
      *
      *  @param[in]  msg - Data associated with subscribed signal