audio, pipewire: fix signatures of pw_get_library_version and pw_init.

Reference issue: https://github.com/libsdl-org/SDL/issues/5938

src/audio/pipewire/SDL_pipewire.c

@@ -86,8 +86,8 @@ enum PW_READY_FLAGS
 static SDL_bool pipewire_initialized = SDL_FALSE;
 
 /* Pipewire entry points */
-static char *(*PIPEWIRE_pw_get_library_version)(void);
-static void (*PIPEWIRE_pw_init)(int *, char **);
+static const char *(*PIPEWIRE_pw_get_library_version)(void);
+static void (*PIPEWIRE_pw_init)(int *, char ***);
 static void (*PIPEWIRE_pw_deinit)(void);
 static struct pw_thread_loop *(*PIPEWIRE_pw_thread_loop_new)(const char *, const struct spa_dict *);
 static void (*PIPEWIRE_pw_thread_loop_destroy)(struct pw_thread_loop *);