tools: Fix clangtidy warning for PpcMemDevice

It seems that the the recently checked in PpcMemDevice code had a
clangtidy issue with the move assignment operator.

Fixing it by deleting the previously defaulted operator as it is
implicitly deleted due to a non-static const data member "ppcMemPath".

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I125cbbb5be6edd53274a9025b741df98cb7f408d
diff --git a/tools/io.hpp b/tools/io.hpp
index 6cc982c..48e70bf 100644
--- a/tools/io.hpp
+++ b/tools/io.hpp
@@ -49,11 +49,11 @@
 
     ~DevMemDevice() = default;
 
-    /* Don't allow copying or assignment, only moving. */
+    /* Don't allow copying, assignment or move assignment, only moving. */
     DevMemDevice(const DevMemDevice&) = delete;
     DevMemDevice& operator=(const DevMemDevice&) = delete;
     DevMemDevice(DevMemDevice&&) = default;
-    DevMemDevice& operator=(DevMemDevice&&) = default;
+    DevMemDevice& operator=(DevMemDevice&&) = delete;
 
     bool read(const std::size_t offset, const std::size_t length,
               void* const destination) override;