[ALSA] Fix unfreed pnp driver in opti9xx ISA driver

[ALSA] Fix unfreed pnp driver in opti9xx ISA driver

- Added the missing pnp_unregister_card_driver() in the case ISA PnP
  isn't found, which caused an error at kobject_add with -EEXIST
   Jun 11 09:07:31 rain kernel: kobject_add failed for opti9xx with -EEXIST, don't try to register things with the same name in the same directory.
   Jun 11 09:07:31 rain kernel:  [<c01c18fa>] kobject_shadow_add+0x12a/0x1c0
   Jun 11 09:07:31 rain kernel:  [<c01c1a81>] kobject_register+0x21/0x50
   Jun 11 09:07:31 rain kernel:  [<c01f09a2>] bus_add_driver+0x72/0x1b0
   Jun 11 09:07:31 rain kernel:  [<c01d3dff>] pnp_register_card_driver+0x4f/0xc0
   Jun 11 09:07:31 rain kernel:  [<c89bc00a>] alsa_card_opti9xx_init+0xa/0x25 [snd_opti92x_ad1848]
   Jun 11 09:07:31 rain kernel:  [<c0136947>] sys_init_module+0x157/0x1610
   Jun 11 09:07:31 rain kernel:  [<c01029b4>] syscall_call+0x7/0xb
- Fixed the probe behavior when no PnP is set up.  Now it behaves
  like the former version.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>