tools/: API change - atrf_open now requires a string argument (can be NULL)

atrf_open(NULL) maintains the old behaviour. To select a driver, use
atrf_open("name") or atrf_open("name:driver-specific-arguments")
The driver name is "ben" or "usb".

- include/atrf.h (atrf_open), lib/atrf.c (do_atrf_open, atrf_open):
  atrf_open now requires the string argument for driver selection
- atrf-id/atrf-id.c (main), atrf-reset/atrf-reset.c (main),
  atrf-rssi/atrf-rssi.c (main), atrf-trim/atrf-trim.c (main),
  atrf-txrx/atrf-txrx.c (main), atrf-xtal/atrf-xtal.c (main):
  changed atrf_open() to atrf_open(NULL)

tools/atrf-trim/atrf-trim.c

@@ -1,8 +1,8 @@
 /*
  * atrf-trim/atrf-trim.c - AT86RF230 oscillator trim utility
  *
- * Written 2010 by Werner Almesberger
- * Copyright 2010 Werner Almesberger
+ * Written 2010-2011 by Werner Almesberger
+ * Copyright 2010-2011 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -44,7 +44,7 @@ int main(int argc, const char **argv)
 		usage(*argv);
 	}
 
-	dsc = atrf_open();
+	dsc = atrf_open(NULL);
 	if (!dsc)
 		return 1;