[media] media: fsl_viu: fix bug in streamon routine

[media] media: fsl_viu: fix bug in streamon routine

Currently video capturing using streaming I/O method
doesn't work if capturing to overlay buffer took place
before.

When enabling the stream we have to check the overlay
enable driver flag and reset it so that the interrupt
handler won't execute the overlay interrupt path after
enabling DMA in streamon routine. Otherwise the capture
interrupt won't be handled correctly causing non working
VIDIOC_DQBUF ioctl.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>