[Bugfix] UnspecifiedOmniPlatform.get_device_count returns 0 instead o… (#3636)

Signed-off-by: princepride <wangzhipeng628@gmail.com>

vllm_omni/platforms/interface.py

@@ -204,3 +204,7 @@ class OmniPlatform(Platform):
 class UnspecifiedOmniPlatform(OmniPlatform):
     _omni_enum = OmniPlatformEnum.UNSPECIFIED
     device_type = ""
+
+    @classmethod
+    def get_device_count(cls) -> int:
+        return 0