ac/nir: do not sign-extend the result of texop_samples_identical

The return value should be a NIR 1-bit bool.

This fixes a regression with piglit
ext_shader_samples_identical-simple-fs 2 on RadeonSI.

Fixes: e690a1b78b ("ac/llvm: don't lower bool to int32, switch to native i1 bool")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7236>

src/amd/llvm/ac_nir_to_llvm.c

@@ -4254,9 +4254,7 @@ static void visit_tex(struct ac_nir_context *ctx, nir_tex_instr *instr)
       result = build_tex_intrinsic(ctx, instr, &txf_args);
 
       result = LLVMBuildExtractElement(ctx->ac.builder, result, ctx->ac.i32_0, "");
-      result = LLVMBuildSExt(ctx->ac.builder,
-                             emit_int_cmp(&ctx->ac, LLVMIntEQ, result, ctx->ac.i32_0),
-                             ctx->ac.i32, "");
+      result = emit_int_cmp(&ctx->ac, LLVMIntEQ, result, ctx->ac.i32_0);
       goto write_result;
    }