remount: Replace ServiceManager::getService with checkService

Address this build log message:
```
[ 18% 2/11] //system/core/fs_mgr:remount clang++ fs_mgr_remount.cpp
system/core/fs_mgr/fs_mgr_remount.cpp:133:31: warning: 'getService' is deprecated: this polls for 5s, prefer waitForService or checkService [-Wdeprecated-declarations]
        if (auto binder = sm->getService(android::String16("vold"))) {
                              ^
```

Bug: 293695109
Test: adb-remount-test
Change-Id: I3b5c7d338e9307dee58edeb0f6a00ba9a73d46f6
diff --git a/fs_mgr/fs_mgr_remount.cpp b/fs_mgr/fs_mgr_remount.cpp
index 4c45828..4b3a5d3 100644
--- a/fs_mgr/fs_mgr_remount.cpp
+++ b/fs_mgr/fs_mgr_remount.cpp
@@ -128,12 +128,11 @@
 }
 
 static android::sp<android::os::IVold> GetVold() {
+    auto sm = android::defaultServiceManager();
     while (true) {
-        if (auto sm = android::defaultServiceManager()) {
-            if (auto binder = sm->getService(android::String16("vold"))) {
-                if (auto vold = android::interface_cast<android::os::IVold>(binder)) {
-                    return vold;
-                }
+        if (auto binder = sm->checkService(android::String16("vold"))) {
+            if (auto vold = android::interface_cast<android::os::IVold>(binder)) {
+                return vold;
             }
         }
         std::this_thread::sleep_for(2s);