[ADT] Fix a comment typo in SmallPtrSet (NFC) (#152565)

In the large mode, SmallPtrSet uses quadratic probing with ProbeAmt++
just like DenseMap.

Author: kazutakahirata

llvm/include/llvm/ADT/SmallPtrSet.h

@@ -46,7 +46,7 @@ namespace llvm {
 /// sets are often small.  In this case, no memory allocation is used, and only
 /// light-weight and cache-efficient scanning is used.
 ///
-/// Large sets use a classic exponentially-probed hash table.  Empty buckets are
+/// Large sets use a classic quadratically-probed hash table.  Empty buckets are
 /// represented with an illegal pointer value (-1) to allow null pointers to be
 /// inserted.  Tombstones are represented with another illegal pointer value
 /// (-2), to allow deletion.  The hash table is resized when the table is 3/4 or