spirv: Make vtn_function a vtn_cf_node

Cherry-pick'd from d94e464a9fc5da334ae224810f855fff6890be50

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3820>
Change-Id: I2a6c4e1bb2fb14da14fd96de9f2f9f31cc4b6c0b
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/403195
Reviewed-by: John Bauman <jbauman@google.com>
3 files changed