yang: fix wrong check for isis metric style

yang: fix wrong check for isis metric style

Before:
```
anlan(config)# route isis ix
anlan(config-router)# metric-style transition
...
anlan(config-if)# isis metric 200
% Configuration failed.

Error type: validation
Error description: YANG error(s):
 Path: Data location "/frr-interface:lib/interface[name='x']/frr-isisd:isis/metric/level-1".
 Error: Must condition ". < 64 or /frr-isisd:isis/instance[area-tag = current()/../../area-tag]/metric-style = 'wide' or not(/frr-isisd:isis/instance[area-tag = current()/../../area-tag]/metric-style)" not satisfied.
 Path: Data location "/frr-interface:lib/interface[name='x']/frr-isisd:isis/metric/level-2".
 Error: Must condition ". < 64 or /frr-isisd:isis/instance[area-tag = current()/../../area-tag]/metric-style = 'wide' or not(/frr-isisd:isis/instance[area-tag = current()/../../area-tag]/metric-style)" not satisfied
```

After:
```
anlan(config)# route isis ix
anlan(config-router)# metric-style transition
...
anlan(config-if)# isis metric 200
anlan(config-if)#
```

Signed-off-by: anlan_cs <anlan_cs@tom.com>