ALSA: portman2x4: fix NULL pointer dereference

While registering pardev, the irq_func was also registered. As a result
when we tried to probe for the card, an interrupt was generated and in
the ISR we tried to dereference private_data. But private_data is still
NULL as we have not yet done portman_create(). Lets probe for the device
after card is created.

Fixes: e6a1b7e8 ("ALSA: portman2x4 - use new parport device model")
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>