[fuchsia] Enable trusted loader service in API Level 28+

This was missed when creating API level 28 and 29. `TrustedService` is
marked `@available(added=28)`.

Bug: 419087951
Change-Id: I1fc67a5c6b2061262e521174d3f4fee5c8c1ce61
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/Vulkan-Loader/+/1399793
Fuchsia-Auto-Submit: David Dorwin <ddorwin@google.com>
Reviewed-by: Craig Stout <cstout@google.com>
Commit-Queue: David Dorwin <ddorwin@google.com>

loader/loader_fuchsia_service.cc

diff --git a/loader/loader_fuchsia_service.cc b/loader/loader_fuchsia_service.cc
index 4686d07..7455a77 100644
--- a/loader/loader_fuchsia_service.cc
+++ b/loader/loader_fuchsia_service.cc
@@ -47,7 +47,7 @@
     fidl::WireSyncClient<fuchsia_vulkan_loader::Loader> client;
     fuchsia_vulkan_loader::wire::Features features;
 
-#if FUCHSIA_API_LEVEL_AT_LEAST(NEXT)
+#if FUCHSIA_API_LEVEL_AT_LEAST(28)
     // Default to the trusted service; if unavailable, fall back to the bare protocol.
     if (auto open_result = component::OpenService<fuchsia_vulkan_loader::TrustedService>(); open_result.is_ok()) {
         fuchsia_vulkan_loader::TrustedService::ServiceClient& service_client = open_result.value();