[calls] ui-call-data: Document calls_call_state_to_cui_call_state()

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit e4dc6548c530cfc035fecbc2f1bbcc8ac9088aa3
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Tue Feb 1 07:36:10 2022 +0100

    ui-call-data: Document calls_call_state_to_cui_call_state()

 src/calls-ui-call-data.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/src/calls-ui-call-data.c b/src/calls-ui-call-data.c
index 895b8f33..3da5d134 100644
--- a/src/calls-ui-call-data.c
+++ b/src/calls-ui-call-data.c
@@ -570,6 +570,12 @@ calls_ui_call_data_get_silenced (CallsUiCallData *self)
 }
 
 
+/**
+ * calls_call_state_to_cui_call_state:
+ * @state: A #CallsCallState
+ *
+ * Returns: a #CuiCallState @state is mapped to.
+ */
 CuiCallState
 calls_call_state_to_cui_call_state (CallsCallState state)
 {