drm/vmwgfx: reorder framebuffer init sequence

vmwgfx has an oddity, when failing to reference the surface it'll
return 0, since that's what the successfull drm_framebuffer_init will
leave behind in ret. Fix this up by returning -EINVAL.

Split out from all the other driver updates due to the above tiny
semantic change. Shouldn't matter though since the reference grabbing
seemingly can't fail.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>