PEL: Rename function that gets RO data path

It was just named after the message registry path, but soon other files
will be in that same directory so make it more generic.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I91117d685aec43f26b9fc6baa2955de3d1affde4
diff --git a/extensions/openpower-pels/manager.hpp b/extensions/openpower-pels/manager.hpp
index 1aa15ed..d58b36b 100644
--- a/extensions/openpower-pels/manager.hpp
+++ b/extensions/openpower-pels/manager.hpp
@@ -51,7 +51,7 @@
         PELInterface(logManager.getBus(), OBJ_LOGGING),
         _logManager(logManager), _eventLogger(std::move(creatorFunc)),
         _repo(getPELRepoPath()),
-        _registry(getMessageRegistryPath() / message::registryFileName),
+        _registry(getPELReadOnlyDataPath() / message::registryFileName),
         _dataIface(std::move(dataIface))
     {
     }