rp2/main: Use mp_printf in nlr_jump_fail.

The mp_plat_print output is already being used by the subsequent call to
mp_obj_print_exception().  And this eliminates all references to printf for
this port (at least in non-debug builds).

Signed-off-by: Damien George <damien@micropython.org>

ports/rp2/main.c

@@ -234,7 +234,7 @@ void gc_collect(void) {
 }
 
 void nlr_jump_fail(void *val) {
-    printf("FATAL: uncaught exception %p\n", val);
+    mp_printf(&mp_plat_print, "FATAL: uncaught exception %p\n", val);
     mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(val));
     for (;;) {
         __breakpoint();