FaderPort8: Use explicit "Port 1" for FP8 too

84e38b4c65 made the same change for FP16.

It has apparently not been necessary for FP8 so far, because backends
have happened to report "Port 1" before the control port. But that is
not necessarily the case. It failed for me when playing around.

Change FP8 handling to also not make assumptions about the device order
returned by the backend.

libs/surfaces/faderport8/faderport8.cc

@@ -117,7 +117,7 @@ FaderPort8::probe (std::string& i, std::string& o)
 #elif defined FADERPORT2
 	    "PreSonus FP2"
 #else
-	    "PreSonus FP8"
+	    "PreSonus FP8 Port 1"
 #endif
 	    ;