Staging: speakup/speakup_acntpc: Return NULL instead of 0

The function returns a pointer. Hence return NULL instead of 0.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/speakup_acntpc.c

@@ -166,7 +166,7 @@ static const char *synth_immediate(struct spk_synth *synth, const char *buf)
 		outb_p(ch, speakup_info.port_tts);
 		buf++;
 	}
-	return 0;
+	return NULL;
 }
 
 static void do_catch_up(struct spk_synth *synth)