test: sysfs: Fix readability-static-accessed-through-instance

```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../test/sysfs.cpp:67:26: error: static member accessed through instance [readability-static-accessed-through-instance,-warnings-as-errors]
            f.exceptions(f.failbit);
                         ^~
                         std::ofstream::
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../test/sysfs.cpp:72:22: error: static member accessed through instance [readability-static-accessed-through-instance,-warnings-as-errors]
        f.exceptions(f.failbit);
                     ^~
                     std::ofstream::
```

Change-Id: I003097a68f17d4ec7ea8dee2e9638d8708770276
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/test/sysfs.cpp b/test/sysfs.cpp
index cc19fc1..3e5172c 100644
--- a/test/sysfs.cpp
+++ b/test/sysfs.cpp
@@ -65,12 +65,12 @@
         {
             fs::path p = root / attr;
             std::ofstream f(p, std::ios::out);
-            f.exceptions(f.failbit);
+            f.exceptions(std::ofstream::failbit);
         }
 
         fs::path p = root / attrMaxBrightness;
         std::ofstream f(p, std::ios::out);
-        f.exceptions(f.failbit);
+        f.exceptions(std::ofstream::failbit);
         f << maxBrightnessVal;
     }
 };