Bugfix: modminer: Return failure to change frequency when device reports it

driver-modminer.c

@@ -336,6 +336,8 @@ modminer_change_clock(struct thr_info*thr, bool needlock, signed char delta)
 
 	if (buf[0])
 		state->dclk.freqM = clk / 2;
+	else
+		return false;
 
 	return true;
 }