ALSA: trident: Suppress gcc string warning

The meddlesome gcc warns about the possible shortname string in
trident driver code:
  sound/pci/trident/trident.c: In function ‘snd_trident_probe’:
  sound/pci/trident/trident.c:126:2: warning: ‘strcat’ accessing 17 or more bytes at offsets 36 and 20 may overlap 1 byte at offset 36 [-Wrestrict]
  strcat(card->shortname, card->driver);

It happens since gcc calculates the possible string size from
card->driver, but this can't be true since we did set the string just
before that, and they are much shorter.

For shutting it up, use the exactly same string set to card->driver
for strcat() to card->shortname, too.

Signed-off-by: Takashi Iwai <tiwai@suse.de>