[RISCV][TTI] Simplify compound check for readability [nfc] (llvm#121504)

I misread this check earlier today on a review, so restructure it to be
easier to quickly scan.

Author: preames

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -2558,8 +2558,10 @@ RISCVTTIImpl::enableMemCmpExpansion(bool OptSize, bool IsZeroCmp) const {
   TTI::MemCmpExpansionOptions Options;
   // TODO: Enable expansion when unaligned access is not supported after we fix
   // issues in ExpandMemcmp.
-  if (!(ST->enableUnalignedScalarMem() &&
-        (ST->hasStdExtZbb() || ST->hasStdExtZbkb() || IsZeroCmp)))
+  if (!ST->enableUnalignedScalarMem())
+    return Options;
+
+  if (!ST->hasStdExtZbb() && !ST->hasStdExtZbkb() && !IsZeroCmp)
     return Options;
 
   Options.AllowOverlappingLoads = true;