Free the correct struct element

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/bignum_new.c b/library/bignum_new.c
index 8a75806..3f25fad 100644
--- a/library/bignum_new.c
+++ b/library/bignum_new.c
@@ -130,7 +130,7 @@
         case MBEDTLS_MPI_MOD_REP_MONTGOMERY:
             mbedtls_free( m->rep.mont ); break;
         case MBEDTLS_MPI_MOD_REP_OPT_RED:
-            mbedtls_free( m->rep.mont ); break;
+            mbedtls_free( m->rep.ored ); break;
         default:
             break;
     }