We need to check returning error for pci_register_driver(&joystick_driver)

On failure, we should unregister formerly registered audio drivers

This also fixed the compiler warning :

  CC [M]  sound/pci/riptide/riptide.o
 sound/pci/riptide/riptide.c: In function ‘alsa_card_riptide_init’:
 sound/pci/riptide/riptide.c:2200: warning: ignoring return value of ‘__pci_register_driver’, declared with attribute warn_unused_result
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>