[analyzer][NFC] Use switch statement in MallocChecker::performKernelMalloc

[steakhal]

It doesn't look much of an improvement TBH, but I won't stand against it either.
LGTM

clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

MallocChecker::performKernelMalloc(const CallEvent &Call, CheckerContext &C,
 
   // This logic is largely cloned from O_CREAT in UnixAPIChecker, maybe some
   // code could be shared.
 
   ASTContext &Ctx = C.getASTContext();
   llvm::Triple::OSType OS = Ctx.getTargetInfo().getTriple().getOS();
 
   if (!KernelZeroFlagVal) {
-    if (OS == llvm::Triple::FreeBSD)
+    switch (OS) {
+    case llvm::Triple::FreeBSD:
       KernelZeroFlagVal = 0x0100;
-    else if (OS == llvm::Triple::NetBSD)
+      break;
+    case llvm::Triple::NetBSD:
       KernelZeroFlagVal = 0x0002;
-    else if (OS == llvm::Triple::OpenBSD)
+      break;
+    case llvm::Triple::OpenBSD:
       KernelZeroFlagVal = 0x0008;
-    else if (OS == llvm::Triple::Linux)
+      break;
+    case llvm::Triple::Linux:
       // __GFP_ZERO
       KernelZeroFlagVal = 0x8000;
-    else
+      break;
+    default:
       // FIXME: We need a more general way of getting the M_ZERO value.
       // See also: O_CREAT in UnixAPIChecker.cpp.
 
       // Fall back to normal malloc behavior on platforms where we don't
       // know M_ZERO.
       return std::nullopt;
     }
+  }
 
   // We treat the last argument as the flags argument, and callers fall-back to
   // normal malloc on a None return. This works for the FreeBSD kernel malloc
   // as well as Linux kmalloc.
   if (Call.getNumArgs() < 2)
     return std::nullopt;
 
   const Expr *FlagsEx = Call.getArgExpr(Call.getNumArgs() - 1);