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/programs/x509/cert_write.c b/programs/x509/cert_write.c
index be32230..2ed63f0 100644
--- a/programs/x509/cert_write.c
+++ b/programs/x509/cert_write.c
@@ -30,7 +30,7 @@
 
 #include "mbedtls/x509_crt.h"
 #include "mbedtls/x509_csr.h"
-#include "mbedtls/private/oid.h"
+#include "mbedtls/oid.h"
 #include "mbedtls/private/entropy.h"
 #include "mbedtls/private/ctr_drbg.h"
 #include "mbedtls/error.h"