intel/fs: Tweak default case of fs_inst::size_read()

In the default case, there's a special case with a few conditions.
Prefer the cheapest conditions first, so we can take advantage of
short-circuiting.

Effect is a small but still significant reduce in shader compilation
times, as can be seen by:

- Fossil replay for Rise of the Tomb Raider

```
Difference at 95.0% confidence
	-0.433333 +/- 0.028609
	-1.42556% +/- 0.0941163%
	(Student's t, pooled s = 0.0337886)
```

- Fossil replay for Batman Arkham City

```
Difference at 95.0% confidence
	-8.84 +/- 0.146083
	-1.65932% +/- 0.0274207%
	(Student's t, pooled s = 0.125423)
```

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25549>

src/intel/compiler/brw_fs.cpp

@@ -911,7 +911,7 @@ fs_inst::size_read(int arg) const
       break;
 
    default:
-      if (is_tex() && arg == 0 && src[0].file == VGRF)
+      if (arg == 0 && src[0].file == VGRF && is_tex())
          return mlen * REG_SIZE;
       break;
    }