Silence GCC fscanf warning in TracySysPower.cpp

fscanf is [[warn_unused_result]], which triggers -Wunused-result. In
this instance it is correct for maxRange to remain unchanged if reading
from sysfs should fail for some reason.

public/client/TracySysPower.cpp

@@ -85,7 +85,7 @@ void SysPower::ScanDirectory( const char* path, int parent )
                 FILE* f = fopen( tmp, "r" );
                 if( f )
                 {
-                    fscanf( f, "%" PRIu64, &maxRange );
+                    (void)fscanf( f, "%" PRIu64, &maxRange );
                     fclose( f );
                 }
             }