nir: add missing break to nir_opt_access()

Fixes: f2d0e48ddc ("glsl/nir: Add optimization pass for access flags")

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5714>

src/compiler/nir/nir_opt_access.c

@@ -120,6 +120,7 @@ gather_intrinsic(struct access_state *state, nir_intrinsic_instr *instr)
 
       _mesa_set_add(state->vars_written, var);
       state->buffers_written = true;
+      break;
 
    case nir_intrinsic_memory_barrier:
       state->buffer_barriers = true;