Use String8/16 c_str [tools]

Bug: 295394788
Test: make checkbuild
Change-Id: I82d6899d8c15a10b15399c39177290012bb5f13b
diff --git a/tools/aapt/ResourceIdCache.cpp b/tools/aapt/ResourceIdCache.cpp
index 8835fb0..1c7788d 100644
--- a/tools/aapt/ResourceIdCache.cpp
+++ b/tools/aapt/ResourceIdCache.cpp
@@ -37,7 +37,7 @@
 
 static uint32_t hash(const android::String16& hashableString) {
     uint32_t hash = 5381;
-    const char16_t* str = hashableString.string();
+    const char16_t* str = hashableString.c_str();
     while (int c = *str++) hash = hashround(hash, c);
     return hash;
 }