GPU-DRM-GMA500: One error message less for a GCT revision mismatch in mid_get_vbt_data()

[SF Markus Elfring]

>> A single error message should be sufficient to inform about
>> the detection of an unknown GCT revision at the end.
>> Thus return after the logging call in this case directly.
> 
> Did you test this?

What is your software development opinion for this update suggestion?

Regards,
Markus