ALSA: core: Allow card id change to the same string

When user want to change the card id to the same string
on the card via /sys/class/sound/cardX/id, do not
report error. Instead return with success without
doing anything.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>