Spelling mistakes in comments. NFCI.

Based on corrections mentioned in patch for clang for PR27635

llvm-svn: 299074
diff --git a/clang-tools-extra/clang-rename/USRFinder.cpp b/clang-tools-extra/clang-rename/USRFinder.cpp
index 7733c6f..d850af5 100644
--- a/clang-tools-extra/clang-rename/USRFinder.cpp
+++ b/clang-tools-extra/clang-rename/USRFinder.cpp
@@ -27,7 +27,7 @@
 
 // NamedDeclFindingASTVisitor recursively visits each AST node to find the
 // symbol underneath the cursor.
-// FIXME: move to seperate .h/.cc file if this gets too large.
+// FIXME: move to separate .h/.cc file if this gets too large.
 namespace {
 class NamedDeclFindingASTVisitor
     : public clang::RecursiveASTVisitor<NamedDeclFindingASTVisitor> {