[gardening] Fix recently introduced typo.

Author: practicalswift

include/swift/AST/Expr.h

@@ -103,7 +103,7 @@ enum class AccessSemantics : unsigned char {
   /// non-polymorphic access to the getter/setter accessors.
   DirectToAccessor,
 
-  /// On a property or subscript reference, this is a access to a property
+  /// On a property or subscript reference, this is an access to a property
   /// behavior that may be an initialization. Reads always go through the
   /// 'get' accessor on the property. Writes may go through the 'init' or
   /// 'set' logic of the behavior based on its initialization state.