Adding root_check before set_override method execution (#524)

This will ensure that set_override calls are always in su mode.
So, in effect all override using 'force' can clearly access
the governer_override_state path file, and write changes to it,
without externally tinkering the environment.

auto_cpufreq/core.py

@@ -96,6 +96,7 @@ def get_override():
         return "default"
 
 def set_override(override):
+    root_check() # Calling root_check inside if and elif might be too verbose and is susceptible to bugs in future
     if override in ["powersave", "performance"]:
         with open(governor_override_state, "wb") as store:
             pickle.dump(override, store)