MDEV-11087 Search path for my.ini is wrong for default installation

Add <install_root>/data/my.ini to the search path -  this my.ini location
is used since MariaDB 5.2

mysys/my_default.c

@@ -90,7 +90,7 @@ static my_bool defaults_already_read= FALSE;
 
 /* Which directories are searched for options (and in which order) */
 
-#define MAX_DEFAULT_DIRS 6
+#define MAX_DEFAULT_DIRS 7
 #define DEFAULT_DIRS_SIZE (MAX_DEFAULT_DIRS + 1)  /* Terminate with NULL */
 static const char **default_directories = NULL;
 
@@ -1219,7 +1219,12 @@ static const char **init_default_directories(MEM_ROOT *alloc)
     errors += add_directory(alloc, "C:/", dirs);
 
     if (my_get_module_parent(fname_buffer, sizeof(fname_buffer)) != NULL)
+    {
+      errors += add_directory(alloc, fname_buffer, dirs);
+
+      strncat(fname_buffer, "/data", sizeof(fname_buffer));
       errors += add_directory(alloc, fname_buffer, dirs);
+    }
   }
 
 #else