staging: bcm2835-camera: Handle empty EOS buffers whilst streaming

staging: bcm2835-camera: Handle empty EOS buffers whilst streaming

The change to mapping V4L2 to MMAL buffers 1:1 didn't handle
the condition we get with raw pixel buffers (eg YUV and RGB)
direct from the camera's stills port. That sends the pixel buffer
and then an empty buffer with the EOS flag set. The EOS buffer
wasn't handled and returned an error up the stack.

Handle the condition correctly by returning it to the component
if streaming, or returning with an error if stopping streaming.

Fixes: 9384167 "staging: bcm2835-camera: Remove V4L2/MMAL buffer remapping"

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>