ALSA: hdsp: fix a test for copy_to_user() failure

The copy_to_user() function returns the number of bytes remaining to be
copied.  It doesn't return negatives.

Fixes: 66c8f759 ("ALSA: hdsp: Fix assignment in if condition")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YNIzqpVR6L2t/RwJ@mwanda


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