media: rockchip: rkcif: Add missing MUST_CONNECT flag to pads

media: rockchip: rkcif: Add missing MUST_CONNECT flag to pads

The pads missed checks for connected devices which may a null dereference
when the stream is enabled.

Unable to handle kernel NULL pointer dereference at virtual address
0000000000000020
pc : rkcif_interface_enable_streams+0x48/0xf0
lr : rkcif_interface_enable_streams+0x44/0xf0
Call trace:
 rkcif_interface_enable_streams+0x48/0xf0
 v4l2_subdev_enable_streams+0x26c/0x3f0
 rkcif_stream_start_streaming+0x140/0x278
 vb2_start_streaming+0x74/0x188
 vb2_core_streamon+0xe0/0x1d8
 vb2_ioctl_streamon+0x60/0xa8
 v4l_streamon+0x2c/0x40
 __video_do_ioctl+0x34c/0x400
 video_usercopy+0x2d0/0x800
 video_ioctl2+0x20/0x60
 v4l2_ioctl+0x48/0x78

Fixes: 501802e2ad51 ("media: rockchip: rkcif: add abstraction for dma blocks")
Fixes: 85411d17bee9 ("media: rockchip: rkcif: add abstraction for interface and crop blocks")
Cc: stable@vger.kernel.org
Signed-off-by: Dang Huynh <dang.huynh@mainlining.org>
Reviewed-by: Michael Riesch <michael.riesch@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>