kfifo: Don't use integer as NULL pointer

This patch fixes following sparse warnings:

include/linux/kfifo.h:127:25: warning: Using plain integer as NULL pointer
kernel/kfifo.c:83:21: warning: Using plain integer as NULL pointer
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/kfifo.h

@@ -124,7 +124,7 @@ extern __must_check unsigned int kfifo_out_peek(struct kfifo *fifo,
  */
 static inline bool kfifo_initialized(struct kfifo *fifo)
 {
-	return fifo->buffer != 0;
+	return fifo->buffer != NULL;
 }
 
 /**

kernel/kfifo.c

@@ -80,7 +80,7 @@ int kfifo_alloc(struct kfifo *fifo, unsigned int size, gfp_t gfp_mask)
 
 	buffer = kmalloc(size, gfp_mask);
 	if (!buffer) {
-		_kfifo_init(fifo, 0, 0);
+		_kfifo_init(fifo, NULL, 0);
 		return -ENOMEM;
 	}