DRM-vmwgfx: Deletion of an unnecessary check before the function call "vfree"

[SF Markus Elfring]

> Reviewed-by: Zhao Junwang <zhjwpku at gmail.com> 
> 
> kfree will check that.

How does this feedback fit to a check before a call
of the vfree() function?

Regards,
Markus