Use StringRef in Datalayout API (NFC)

llvm-svn: 283013
diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
index 27d2c4b..b73225e 100644
--- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -939,7 +939,7 @@
 
 //===----------------------------------------------------------------------===//
 
-static MCSymbol *getPICLabel(const char *Prefix, unsigned FunctionNumber,
+static MCSymbol *getPICLabel(StringRef Prefix, unsigned FunctionNumber,
                              unsigned LabelId, MCContext &Ctx) {
 
   MCSymbol *Label = Ctx.getOrCreateSymbol(Twine(Prefix)