Fix modules/ typos

Found using `codespell -q 3 -S ./3rdparty -L activ,amin,ang,atleast,childs,dof,endwhile,halfs,hist,iff,nd,od,uint`

backporting of commit: ec43292e1e

modules/flann/include/opencv2/flann/hierarchical_clustering_index.h

@@ -578,7 +578,7 @@ public:
 private:
 
     /**
-     * Struture representing a node in the hierarchical k-means tree.
+     * Structure representing a node in the hierarchical k-means tree.
      */
     struct Node
     {

modules/flann/include/opencv2/flann/kmeans_index.h

@@ -547,7 +547,7 @@ public:
 
 private:
     /**
-     * Struture representing a node in the hierarchical k-means tree.
+     * Structure representing a node in the hierarchical k-means tree.
      */
     struct KMeansNode
     {

modules/flann/include/opencv2/flann/result_set.h

@@ -301,7 +301,7 @@ public:
         unsigned int index_;
     };
 
-    /** Default cosntructor */
+    /** Default constructor */
     UniqueResultSet() :
         is_full_(false), worst_distance_(std::numeric_limits<DistanceType>::max())
     {