Don't depend on String8 cast to C string

Bug: 295394788
Test: m checkbuild
Change-Id: I5b86ae56250d409a23ab3f2bc72b725bcf6ab23e
diff --git a/libutils/CallStack.cpp b/libutils/CallStack.cpp
index 4dcb35b..11f2c92 100644
--- a/libutils/CallStack.cpp
+++ b/libutils/CallStack.cpp
@@ -82,7 +82,7 @@
 
 void CallStack::print(Printer& printer) const {
     for (size_t i = 0; i < mFrameLines.size(); i++) {
-        printer.printLine(mFrameLines[i]);
+        printer.printLine(mFrameLines[i].c_str());
     }
 }