tools: io: add ppcMemFd cleanup

The destructor may try to double-close because the ppcMemFd was not
being set to -1.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I3423ae874d551b39f3deb761c5572078b07a0349
diff --git a/tools/io.hpp b/tools/io.hpp
index 1476c5c..b3b2c79 100644
--- a/tools/io.hpp
+++ b/tools/io.hpp
@@ -91,6 +91,8 @@
                const void* const source) override;
 
   private:
+    void close();
+
     int ppcMemFd = -1;
     const std::string ppcMemPath;
     const internal::Sys* sys;