intel/compiler: Change selected_simd return type to int.

brw_simd_select return type is int.

Fix defect reported by Coverity Scan.

Unsigned compared against 0 (NO_EFFECT)
unsigned_compare: This less-than-zero comparison of an unsigned value is never true. selected_simd < 0U.

Fixes: 7dda0cf2b8 ("intel/compiler: Use SIMD selection helpers for CS")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13606>

src/intel/compiler/brw_fs.cpp

@@ -10146,7 +10146,7 @@ brw_compile_cs(const struct brw_compiler *compiler,
       }
    }
 
-   const unsigned selected_simd = brw_simd_select(prog_data);
+   const int selected_simd = brw_simd_select(prog_data);
    if (selected_simd < 0) {
       params->error_str = ralloc_asprintf(mem_ctx, "Can't compile shader: %s, %s and %s.\n",
                                           error[0], error[1], error[2]);;