Staging: speakup: Return NULL instead of 0 in speakup_decpc.c

The function returns a pointer. Hence return NULL instead of 0.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/speakup_decpc.c

@@ -444,7 +444,7 @@ static const char *synth_immediate(struct spk_synth *synth, const char *buf)
 			return buf;
 		buf++;
 	}
-	return 0;
+	return NULL;
 }
 
 static int synth_probe(struct spk_synth *synth)