Update name of mbedtls_mpi_montg_init()

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/library/bignum_core.c b/library/bignum_core.c
index bb6e7cd..fa7fc85 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -377,7 +377,7 @@
 /*
  * Fast Montgomery initialization (thanks to Tom St Denis).
  */
-mbedtls_mpi_uint mbedtls_mpi_montg_init( const mbedtls_mpi_uint *N )
+mbedtls_mpi_uint mbedtls_mpi_core_montmul_init( const mbedtls_mpi_uint *N )
 {
     mbedtls_mpi_uint x = N[0];