media: ti-vpe: vpe: Remove unnecessary use of container_of

Instead of saving a pointer to the 'fh' member of struct vpe_ctx to
later have to use container_of to retrieve the actual pointer to the
context structure, which seems to confuse static code analysis tool
anyways, just save the pointer to the actual structure and then retrieve
it directly.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>