Unfortunately, we had two files named oid.h - one in the main repo, and one in the tf-psa-crypto repo, and these files included the mbedtls one, so I restored the header include

Signed-off-by: Anton Matkin <anton.matkin@arm.com>
diff --git a/library/x509write.c b/library/x509write.c
index 1d4d556..0906a5a 100644
--- a/library/x509write.c
+++ b/library/x509write.c
@@ -11,7 +11,7 @@
 #include "mbedtls/x509_crt.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/error.h"
-#include "mbedtls/private/oid.h"
+#include "mbedtls/oid.h"
 #include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"