Return a non-zero exit code if an error occurs during dts parsing.

Previously, only failure to parse caused the reading of the tree to fail;
semantic errors that called yyerror() but not YYERROR only emitted a message,
without signalling make to stop the build.

Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/dtc.h b/dtc.h
index 9b89689..cba9d28 100644
--- a/dtc.h
+++ b/dtc.h
@@ -233,6 +233,7 @@
 struct boot_info {
 	struct reserve_info *reservelist;
 	struct node *dt;		/* the device tree */
+	int error;
 };
 
 struct boot_info *build_boot_info(struct reserve_info *reservelist,