hostdev: Remove temporary variable when checking for VF

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.