Staging: speakup: Fix return value in synth.c

The function return type is 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>
diff --git a/drivers/staging/speakup/synth.c b/drivers/staging/speakup/synth.c
index e2d84c0..0b3549b 100644
--- a/drivers/staging/speakup/synth.c
+++ b/drivers/staging/speakup/synth.c
@@ -157,7 +157,7 @@
 			return buff;
 		buff++;
 	}
-	return 0;
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(spk_synth_immediate);