ALSA: riptide - Fix detection / load of firmware files

The detection and loading of firmeware on riptide driver has been broken
due to rewrite of some codes, checking the presense wrongly.
This patch fixes the logic again.

Reference: kernel bug 16596
	https://bugzilla.kernel.org/show_bug.cgi?id=16596



Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>