hostdev: Remove temporary variable when checking for VF
    
    The virHostdevIsVirtualFunction() was called exactly twice, and in
    both cases the return value was saved to a temporary variable before
    being checked. This would be okay if it improved readability, but in
    this case is pretty pointless.
    
    Get rid of the temporary variable and check the return value
    directly; while at it, change the check from '<= 0' to '!= 1' to
    align it with the way other similar *IsVirtualFunction() functions
    are used thorough the code.