V4L/DVB (6060): ivtv: fix IVTV_IOC_DMA_FRAME bug introduced by highmem bugfix

The return value of ivtv_udma_fill_sg_list() was changed by the
highmem bugfix, but that return value was still used in ivtv-yuv.c.

Revert to the old return value, but in addition return -1 in case of
a memory allocation error.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>