ac/llvm: Use nir_foreach_phi

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Konstantin Seurer <konstantin.seurer@gmail.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22967>

src/amd/llvm/ac_nir_to_llvm.c

@@ -4845,10 +4845,8 @@ static bool visit_block(struct ac_nir_context *ctx, nir_block *block)
       LLVMPositionBuilderBefore(ctx->ac.builder, LLVMGetFirstInstruction(blockref));
    }
 
-   nir_foreach_instr(instr, block) {
-      if (instr->type != nir_instr_type_phi)
-         break;
-      visit_phi(ctx, nir_instr_as_phi(instr));
+   nir_foreach_phi(phi, block) {
+      visit_phi(ctx, phi);
    }
 
    LLVMPositionBuilderAtEnd(ctx->ac.builder, blockref);