linux-user: fail and report on bad dfilter specs

Just passing NULL means we end up ignoring the bad dfilter spec
instead of reporting it and exiting as we should.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20190830143648.2967-1-alex.bennee@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/main.c

@@ -235,7 +235,7 @@ static void handle_arg_log(const char *arg)
 
 static void handle_arg_dfilter(const char *arg)
 {
-    qemu_set_dfilter_ranges(arg, NULL);
+    qemu_set_dfilter_ranges(arg, &error_fatal);
 }
 
 static void handle_arg_log_filename(const char *arg)