nir: Fix qsort comparator function

`pred` is a pointer, for sufficiently large numbers these
being cast to int were both > 0 regardless of the order
of `data1` and `data2`.

Fixes: 523a28d3fe ("nir: add an instruction set API")

Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19539>
(cherry picked from commit c987a727a7)

.pick_status.json

@@ -679,7 +679,7 @@
         "description": "nir: Fix qsort comparator function",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "523a28d3fe0dd371ae01b7353f263a6541480d89"
     },

src/compiler/nir/nir_instr_set.c

@@ -212,7 +212,7 @@ cmp_phi_src(const void *data1, const void *data2)
 {
    nir_phi_src *src1 = *(nir_phi_src **)data1;
    nir_phi_src *src2 = *(nir_phi_src **)data2;
-   return src1->pred - src2->pred;
+   return src1->pred > src2->pred ? 1 : (src1->pred == src2->pred ? 0 : -1);
 }
 
 static uint32_t