MdeModulePkg SmiHandlerProfile: Fix memory leak in DumpSmiChildContext

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=530

In DumpSmiChildContext() of SmiHandlerProfile.c and
SmiHandlerProfileInfo.c, the return buffer from
ConvertDevicePathToText() should be freed after used.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>