unicode/norm: fix function name on comment

Change-Id: I1d7daf1101c289f99367db2b23105e99d7e19b65
Reviewed-on: https://go-review.googlesource.com/c/text/+/523255
Run-TryBot: shuang cui <imcusg@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Joedian Reid <joedian@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>

unicode/norm/trie.go

@@ -29,7 +29,7 @@ var (
 	nfkcData = newNfkcTrie(0)
 )
 
-// lookupValue determines the type of block n and looks up the value for b.
+// lookup determines the type of block n and looks up the value for b.
 // For n < t.cutoff, the block is a simple lookup table. Otherwise, the block
 // is a list of ranges with an accompanying value. Given a matching range r,
 // the value for b is by r.value + (b - r.lo) * stride.