plist: fix PLIST_NODE_INIT to work with debug enabled

It seems that PLIST_NODE_INIT breaks if used and DEBUG_PI_LIST is defined.
Since there are no current users of PLIST_NODE_INIT, this has gone
undetected.  This patch fixes the build issue that enables the
DEBUG_PI_LIST later in the series when we use it in init_task.h

Signed-off-by: Gregory Haskins <ghaskins@novell.com>