ALSA: ac97: bus: Add missing module description

Now that make W=1 starts complaining the lack of MODULE_DESCRIPTION(),
let's add the missing information.
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Closes: https://lore.kernel.org/r/ZjpQm-hxLQtpgkUx@smile.fi.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/20240508091128.25274-3-tiwai@suse.de

sound/ac97/bus.c

@@ -551,5 +551,6 @@ static void __exit ac97_bus_exit(void)
 }
 module_exit(ac97_bus_exit);
 
+MODULE_DESCRIPTION("AC97 bus interface");
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Robert Jarzmik <robert.jarzmik@free.fr>");