staging/vc04_services: Resolve merge issue over atomic_inc/dec

e59fc3ed "staging: bcm2835_camera: Ensure all buffers are returned on
disable" was upstreamed and then backported to 4.19 as fcbc6ddc.
In merging that upstream update back into our tree, the merge
has failed and we have ended up with duplication of the lines.

Fix up this merge issue.

https://github.com/raspberrypi/linux/issues/3124



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