elf-core: correct "no sections" to "no segments."

The error reported here is that there are no phdr entries, so it's
referring to segments, not sections.

llvm-svn: 230227

lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp

@@ -191,7 +191,7 @@ ProcessElfCore::DoLoadCore ()
     const uint32_t num_segments = core->GetProgramHeaderCount();
     if (num_segments == 0)
     {
-        error.SetErrorString ("core file has no sections");
+        error.SetErrorString ("core file has no segments");
         return error;
     }