[SandboxVectorizer] Use llvm::find (NFC)

llvm::find allows us to pass a range.

Author: kazutakahirata

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h

@@ -68,7 +68,7 @@ class SeedBundle {
   /// the seeds in a bundle. This allows constant time evaluation
   /// and "removal" from the list.
   void setUsed(Instruction *I) {
-    auto It = std::find(begin(), end(), I);
+    auto It = llvm::find(*this, I);
     assert(It != end() && "Instruction not in the bundle!");
     auto Idx = It - begin();
     setUsed(Idx, 1, /*VerifyUnused=*/false);