media: omap3isp: Unregister media device as first

[ Upstream commit 30efae3d789cd0714ef795545a46749236e29558 ]

While there are issues related to object lifetime management, unregister the
media device first when the driver is being unbound. This is slightly
safer.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>