Fixed correct APM detection

Correct USB descriptor of Arduino Mega (And all my APM's) is:
  iManufacturer           1 Arduino (www.arduino.cc)
  iProduct                2 Arduino Mega 2560

with the M in uppercase, so on my linux system (ArchLinux), I got "Connected to a NON-APM or 3DR Radio with description:". This fix corrects that.