i965/miptree: Fix handling of uninitialized MCS buffers

i965/miptree: Fix handling of uninitialized MCS buffers

Before this patch, if we failed to initialize an MCS buffer, we'd
end up in a state in which the miptree thinks it has an MCS buffer,
but doesn't. We also leaked the clear_color_bo if it existed.

With this patch, we now free the miptree aux buffer resources and let
intel_miptree_alloc_mcs() know that the MCS buffer no longer exists.

Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>