media: ti-vpe: vip: fix leak with v4l2_ctrl_handler

VIP driver creates a v4l2_ctrl_handler for both slices, and the second
one overwrites the pointer to the first, causing a leak. There's
supposed to be a single v4l2_ctrl_handler for a v4l2 driver, so lets
move v4l2_ctrl_handler out from struct vip_dev to struct vip_shared.

Also add call to v4l2_ctrl_handler_free() so that the handler is freed.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Benoit Parrot <bparrot@ti.com>