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/test/openpower-pels/pel_manager_test.cpp b/test/openpower-pels/pel_manager_test.cpp
index 00427c2..92713e9 100644
--- a/test/openpower-pels/pel_manager_test.cpp
+++ b/test/openpower-pels/pel_manager_test.cpp
@@ -208,7 +208,7 @@
 }
 )";
 
-    auto path = getMessageRegistryPath();
+    auto path = getPELReadOnlyDataPath();
     fs::create_directories(path);
     path /= "message_registry.json";