Fix LMS internal function documentation

Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/library/lms.c b/library/lms.c
index 296adce..321e51a 100644
--- a/library/lms.c
+++ b/library/lms.c
@@ -491,7 +491,7 @@
  *
  *  leaf_node_id        Which leaf node to calculate the path from.
  *
- *  tree                The output path, which is H hash outputs.
+ *  path                The output path, which is H hash outputs.
  */
 static int get_merkle_path( mbedtls_lms_private_t *ctx,
                             unsigned int leaf_node_id,