media: ti: j721e-csi2rx: Fix races while restarting DMA

After the frame is submitted to DMA, it may happen that the submitted
list is not updated soon enough, and the DMA callback is triggered
before that.

This can lead to kernel crashes, so move everything in a single
lock/unlock section to prevent such races.

Fixes: b4a3d877 ("media: ti: Add CSI2RX support for J721E")
Signed-off-by: Jai Luthra <j-luthra@ti.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>