dtc: Use va_end to match corresponding va_start

Although on some systems va_end is a no-op, it is good practice
to use va_end, especially since the manual states:

"Each invocation of va_start() must be matched by a corresponding
invocation of va_end() in the same function."

Signed-off-by: Colin Ian King <colin.king@canonical.com>
diff --git a/checks.c b/checks.c
index 3bf0fa4..e81a8c7 100644
--- a/checks.c
+++ b/checks.c
@@ -113,6 +113,7 @@
 		vfprintf(stderr, fmt, ap);
 		fprintf(stderr, "\n");
 	}
+	va_end(ap);
 }
 
 #define FAIL(c, ...) \
diff --git a/util.h b/util.h
index ccfdf4b..f800b60 100644
--- a/util.h
+++ b/util.h
@@ -34,6 +34,7 @@
 	va_start(ap, str);
 	fprintf(stderr, "FATAL ERROR: ");
 	vfprintf(stderr, str, ap);
+	va_end(ap);
 	exit(1);
 }