ir3: Set branchstack earlier

We were relying on it in RA to tell us whether we could give more
registers to the shader mostly "for free" (because occupancy is bounded
by the branchstack), but it turns out it was actually 0 so we weren't
taking advantage of it.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22072>

src/freedreno/ir3/ir3_compiler_nir.c

@@ -4687,6 +4687,8 @@ ir3_compile_shader_nir(struct ir3_compiler *compiler,
       goto out;
    }
 
+   so->branchstack = ctx->max_stack;
+
    ir = so->ir = ctx->ir;
 
    if (gl_shader_stage_is_compute(so->type)) {
@@ -5055,8 +5057,6 @@ ir3_compile_shader_nir(struct ir3_compiler *compiler,
       ir3_instr_move_before(unlock, end);
    }
 
-   so->branchstack = ctx->max_stack;
-
    so->pvtmem_size = ALIGN(so->pvtmem_size, compiler->pvtmem_per_fiber_align);
 
    /* Note that max_bary counts inputs that are not bary.f'd for FS: */