mesa: tidy up renderbuffer RefCount initialisation

42aaa548 changed the renderbuffer initialisation of RefCount from
1 to 0.

This is inconsitent with how we use RefCount elsewhere. Also every
driver implementation of NewRenderbuffer() calls
_mesa_init_renderbuffer() so its safe to set it there.

Reviewed-by: Brian Paul <brianp@vmware.com>
3 files changed