AP_RCMapper: Fix sub only documentation on channels

libraries/AP_RCMapper/AP_RCMapper.cpp

@@ -45,7 +45,7 @@ const AP_Param::GroupInfo RCMapper::var_info[] = {
     // @Increment: 1
     // @User: Advanced
     // @RebootRequired: True
-    // @Values{Sub}: 1-8
+    // @Values{Sub}: 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8
     AP_GROUPINFO_FRAME("FORWARD",    4, RCMapper, _ch_forward, 6, AP_PARAM_FRAME_SUB),
 
     // @Param: LATERAL
@@ -55,7 +55,7 @@ const AP_Param::GroupInfo RCMapper::var_info[] = {
     // @Increment: 1
     // @User: Advanced
     // @RebootRequired: True
-    // @Values{Sub}: 1-8
+    // @Values{Sub}: 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8
     AP_GROUPINFO_FRAME("LATERAL",    5, RCMapper, _ch_lateral, 7, AP_PARAM_FRAME_SUB),
 
     AP_GROUPEND