[media] dt3155v4l: remove pointless dt3155_alloc/free_coherent

No idea what the purpose is of these functions. I suspect this was used
once upon a time to pre-allocate buffer memory. But the allocated memory
isn't used anywhere anymore, so just remove this code.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>