Fix sparse warning: Using plain integer as NULL pointer

This patch fixes the "using plain integer as NULL pointer" warnings
generated by running sparse on the flashrom source.

Corresponding to flashrom svn r1255.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Mathias Krause <mathias.krause@secunet.com>
Acked-by: Stefan Reinauer <stepan@coreboot.org>
diff --git a/cbtable.c b/cbtable.c
index dbb2cff..f30a3ae 100644
--- a/cbtable.c
+++ b/cbtable.c
@@ -141,7 +141,7 @@
 
 	};
 
-	return 0;
+	return NULL;
 }
 
 static void find_mainboard(struct lb_record *ptr, unsigned long addr)