AArch64: Canonicalize access to function attributes, NFC

Canonicalize access to function attributes to use the simpler API.

getAttributes().getAttribute(AttributeSet::FunctionIndex, Kind)
  => getFnAttribute(Kind)

getAttributes().hasAttribute(AttributeSet::FunctionIndex, Kind)
  => hasFnAttribute(Kind)

llvm-svn: 229218
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index e144609..84bf317 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -64,8 +64,7 @@
     return false;
   // Don't use the red zone if the function explicitly asks us not to.
   // This is typically used for kernel code.
-  if (MF.getFunction()->getAttributes().hasAttribute(
-          AttributeSet::FunctionIndex, Attribute::NoRedZone))
+  if (MF.getFunction()->hasFnAttribute(Attribute::NoRedZone))
     return false;
 
   const MachineFrameInfo *MFI = MF.getFrameInfo();