Improve and fix compile initializers for ECDH/ECP

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
diff --git a/tf-psa-crypto/drivers/builtin/include/mbedtls/bignum.h b/tf-psa-crypto/drivers/builtin/include/mbedtls/bignum.h
index 22d5d84..40b7277 100644
--- a/tf-psa-crypto/drivers/builtin/include/mbedtls/bignum.h
+++ b/tf-psa-crypto/drivers/builtin/include/mbedtls/bignum.h
@@ -238,7 +238,7 @@
 }
 mbedtls_mpi;
 
-#define MBEDTLS_MPI_INIT { 0, 0, 0 }
+#define MBEDTLS_MPI_INIT { 0, 1, 0 }
 
 /**
  * \brief           Initialize an MPI context.