Fixed not compiling when using 27xx profile

I'm not sure if this is the correct fix but without this one line the code wouldn't compile and it would say that "data" wasn't declared.

TommyPROM/PromDevice27.cpp

@@ -85,6 +85,7 @@ bool PromDevice27::burnByte(byte value, uint32_t address)
     bool status = false;
     unsigned writeCount = 0;
 
+    byte data = 0;
     disableOutput();
     disableWrite();
     enableChip();