media: isi: fix boot warning by intialize device_caps

commit 6f397e8ab2fa02b99233178531ad0fb8bc829ebe from
https://github.com/nxp-imx/linux-imx

Caused by:
049e684f media: v4l2-dev: fix WARN_ON(!vdev->device_caps)
3c135050

 media: v4l2-dev/ioctl: require non-zero device_caps, verify sane querycap results

[    2.085781] WARNING: CPU: 2 PID: 32 at ../drivers/media/v4l2-core/v4l2-dev.c:864 __video_register_device+0x70/0x1524
[    2.096305] Modules linked in:
[    2.099369] CPU: 2 PID: 32 Comm: kworker/2:1 Not tainted 5.3.0-rc2-next-20190730-01098-g446d4cd #475
[    2.108500] Hardware name: Freescale i.MX8QM MEK (DT)
[    2.113559] Workqueue: events deferred_probe_work_func
[    2.118703] pstate: 60000005 (nZCv daif -PAN -UAO)
[    2.123495] pc : __video_register_device+0x70/0x1524
[    2.128466] lr : __video_register_device+0x70/0x1524
[    2.133433] sp : ffff000011d8b9d0
[    2.136742] x29: ffff000011d8b9d0 x28: ffff8008ff45edc0
[    2.142057] x27: ffff8008f6f35580 x26: ffff000011b2b148
[    2.147374] x25: ffff8008f6e381c0 x24: 0000000000000001
[    2.152691] x23: 0000000000000000 x22: ffff8008f6f35818
[    2.158008] x21: ffff8008f6e381c0 x20: 0000000000000001
[    2.163324] x19: ffff000011989000 x18: ffff000011cfdfff
[    2.168641] x17: 0000000000000000 x16: ffff000011cfdfff
[    2.173958] x15: ffff7e0023dbecc0 x14: 0000000000000000
[    2.179274] x13: 0000000000000000 x12: 0000000000000028
[    2.184591] x11: 0101010101010101 x10: 00000000000009a0
[    2.189908] x9 : ffff000011d8b700 x8 : ffff8008f813c100
[    2.195225] x7 : 0000000000000002 x6 : 00000000000000ed
[    2.200533] x5 : 0000000000000000 x4 : 000000000199047f
[    2.205849] x3 : 0000000000000001 x2 : ddfc02a91bc52500
[    2.211166] x1 : 0000000000000000 x0 : 0000000000000024
[    2.216488] Call trace:
[    2.218940]  __video_register_device+0x70/0x1524
[    2.223563]  mxc_isi_subdev_registered+0x1f8/0x230
[    2.228357]  v4l2_device_register_subdev+0xb0/0x160
[    2.233236]  mxc_md_probe+0x2b0/0x6b8
[    2.236897]  platform_drv_probe+0x4c/0xb0
[    2.240907]  really_probe+0x1c4/0x2d0
[    2.244571]  driver_probe_device+0x58/0xfc
[    2.248665]  __device_attach_driver+0x90/0xac
[    2.253020]  bus_for_each_drv+0x68/0xbc
[    2.256855]  __device_attach+0xe0/0x138
[    2.260686]  device_initial_probe+0x10/0x18
[    2.264867]  bus_probe_device+0x90/0x98
[    2.268696]  deferred_probe_work_func+0x70/0xa4
[    2.273230]  process_one_work+0x13c/0x2b4
[    2.277236]  worker_thread+0x35c/0x3e4
[    2.280985]  kthread+0xf8/0x124
[    2.284132]  ret_from_fork+0x10/0x18

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>