vrend: Don't free resource struct in _resource_allocate_texture

The structure is allocated outside this function and also deleted there
if texture creation failes or it is asserted that it doesn't fail
for intermediate blitting textures. Therefore, don't free the struct inside
this function when allocation fails.

Closes #154

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>