nak: Add Src::is_unmodified() helper

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Fixes: bad23ddb48 ("nak: Add F16 and F16v2 sources")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34794>
(cherry picked from commit 6e72f0f81b05a02341fb68c9d6de96c33ec5ca96)

.pick_status.json

@@ -104,7 +104,7 @@
         "description": "nak: Add Src::is_unmodified() helper",
         "nominated": true,
         "nomination_type": 2,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "bad23ddb4849908a648d503a615a5a9b15e9768a",
         "notes": null

src/nouveau/compiler/nak/ir.rs

@@ -1094,6 +1094,10 @@ impl Src {
         b.into()
     }
 
+    pub fn is_unmodified(&self) -> bool {
+        self.src_mod.is_none() && self.src_swizzle.is_none()
+    }
+
     pub fn fabs(&self) -> Src {
         Src {
             src_ref: self.src_ref,
@@ -1131,7 +1135,7 @@ impl Src {
             return *self;
         };
 
-        if self.src_mod.is_none() && self.src_swizzle.is_none() {
+        if self.is_unmodified() {
             return *self;
         }