Update and fix some issues in EXT-REFERENCE documentation (#5180)

There was some issues and typos in the EXT-REFERENCE documentation.
This patch fixes these issues and typos.

JerryScript-DCO-1.0-Signed-off-by: Gergo Csizi gergocs@inf.u-szeged.hu

docs/12.EXT-REFERENCE-MODULE.md

@@ -63,7 +63,7 @@ to `jerryx_module_resolve` with a module name whose canonical name matches an al
 ```c
 jerry_value_t
 jerryx_module_resolve (const jerry_value_t name,
-                       const jerryx_module_resolver_t *resolvers_p,
+                       const jerryx_module_resolver_t **resolvers_p,
                        size_t resolver_count);
 ```
 
@@ -84,7 +84,7 @@ Remove a module from the current context's cache, or clear the cache entirely.
 ```c
 void
 jerryx_module_clear_cache (const jerry_value_t name,
-                           const jerryx_module_resolver_t *resolvers_p,
+                           const jerryx_module_resolver_t **resolvers_p,
                            size_t resolver_count);
 ```