TT#28460 Fix customer balances get-put use case

Ratio precision is out of boundaries
Set ratio readonly, so it will be deleted on form validation

Change-Id: I729abc05c922682e44d85191b0d78e9d904a5fad
(cherry picked from commit a72f2126ed)

lib/NGCP/Panel/Form/Balance/CustomerBalanceAPI.pm

@@ -37,6 +37,7 @@ has_field 'free_time_spent' => (
 has_field 'ratio' => (
     type => 'Float',
     required => 0,
+    readonly => 1,
     #precision => 6,
     #decimal_symbol => '.',
     element_attr => {