Fix unchecked return in bignum

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix_bignum_unchecked_return.txt b/ChangeLog.d/fix_bignum_unchecked_return.txt
new file mode 100644
index 0000000..1c32da8
--- /dev/null
+++ b/ChangeLog.d/fix_bignum_unchecked_return.txt
@@ -0,0 +1,2 @@
+Bugfix
+   * Fix unchecked return in bignum module.
diff --git a/library/bignum.c b/library/bignum.c
index bfca43d..225e36c 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1666,8 +1666,7 @@
      * calculating the result is trivial in those cases. */
     if( b == 0 || n == 0 )
     {
-        mbedtls_mpi_lset( X, 0 );
-        return( 0 );
+        return mbedtls_mpi_lset( X, 0 );
     }
 
     /* Calculate A*b as A + A*(b-1) to take advantage of mpi_mul_hlp */