ALSA: asihpi: fix an information leak in asihpi_hpi_ioctl()

Add missing limits to keep copied data within allocated buffer.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eliot Blennerhassett <eliot@blennerhassett.gen.nz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>