media: vivid: fix compile warning/error

Fix this warning:

vivid-core.c: In function 'vivid_create_devnodes':
vivid-core.c:1318:11: warning: unused variable 'i' [-Wunused-variable]
 1318 |  int ret, i;
      |           ^

and this error:

vivid-core.c: In function 'vivid_create_instance':
vivid-core.c:1885:47: error: 'cec_tx_bus_cnt' undeclared (first use in this function)
 1885 |  ret = vivid_create_devnodes(pdev, dev, inst, cec_tx_bus_cnt,
      |                                               ^~~~~~~~~~~~~~
vivid-core.c:1885:47: note: each undeclared identifier is reported only once for each function it appears in

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>