pnor_partition_table: Make writeDefaults() private to namespace

This is part of the ongoing effort to extract parseTocLine() from the
Table class, enabling reuse in setup for test cases.

Change-Id: I0b888c028c61db2a555fa99a5abcbe339e657f95
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/pnor_partition_table.cpp b/pnor_partition_table.cpp
index 871adbe..997876d 100644
--- a/pnor_partition_table.cpp
+++ b/pnor_partition_table.cpp
@@ -136,7 +136,7 @@
     part.data.user.data[1] |= version;
 }
 
-inline void Table::writeDefaults(pnor_partition& part)
+static inline void writeDefaults(pnor_partition& part)
 {
     part.data.pid = PARENT_PATITION_ID;
     part.data.type = PARTITION_TYPE_DATA;