media: staging: media: hantro: Remove call to memset after dma_alloc_coherent

fix below issue reported by coccicheck
/drivers/staging/media/hantro/hantro_vp8.c:149:16-34: WARNING:
dma_alloc_coherent use in aux_buf -> cpu already zeroes out memory,  so
memset is not needed

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>