Move SensorSubTree declaration to ipmi scope

Move SensorSubTree declaration to ipmi scope
Issue: Unable to resolve this symbol during loading of this
library, which is due to definition & declaration being in different
scope.

Unit-Test:
Verified that library is loaded properly and ipmitool sensor list
works.

Change-Id: I243e0033d0b76a14c0976f16bd6b893c0e96cb55
Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
diff --git a/include/sensorcommands.hpp b/include/sensorcommands.hpp
index 6135105..66536c2 100644
--- a/include/sensorcommands.hpp
+++ b/include/sensorcommands.hpp
@@ -133,6 +133,8 @@
     ipmiCmdSetSensorReadingAndEventStatus = 0x30,
 };
 
+namespace ipmi
+{
 extern SensorSubTree sensorTree;
 static ipmi_ret_t getSensorConnection(uint8_t sensnum, std::string &connection,
                                       std::string &path)
@@ -164,3 +166,4 @@
 
     return 0;
 }
+} // namespace ipmi