Fixed const correctness issues that have no impact on the ABI
(cherry picked from commit eae09db9e57b7a342ea15bf57c5c1439c59a2e50)

Conflicts:
	library/gcm.c
diff --git a/library/error.c b/library/error.c
index 7f13067..32d9cf1 100644
--- a/library/error.c
+++ b/library/error.c
@@ -27,6 +27,8 @@
 
 #if defined(POLARSSL_ERROR_C)
 
+#include "polarssl/error.h"
+
 #if defined(POLARSSL_AES_C)
 #include "polarssl/aes.h"
 #endif