PNOR Serialize: Change create_directory to create_directories

Core dumps were observed when serialize attempts to create the
directory /var/lib/obmc/openpower-pnor-code-mgmt because the parent
directory /var/lib/obmc did not exist. This commit changes the
create_directory call to create_directories so that any missing
parent directories will be created.

Change-Id: I051fb854b4bf770abec8e0f03f74c194339cc227
Signed-off-by: Michael Tritz <mtritz@us.ibm.com>
diff --git a/serialize.cpp b/serialize.cpp
index 8c63264..ddfede2 100644
--- a/serialize.cpp
+++ b/serialize.cpp
@@ -17,7 +17,7 @@
 {
     if(!fs::is_directory(PERSIST_DIR))
     {
-        fs::create_directory(PERSIST_DIR);
+        fs::create_directories(PERSIST_DIR);
     }
 
     // store one copy in /var/lib/obmc/openpower-pnor-code-mgmt/[versionId]