[media] media: imx: Drop warning upon multiple S_STREAM disable calls

Calling S_STREAM OFF multiple times on a video device is valid, although
dubious, practice. Instead of warning about it and setting stream count
lower than zero, just ignore the subsequent S_STREAM calls and correct
the stream count to zero.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>