api: devices: document HTTP 400 in  deployments/next
api: devices: document HTTP 400 in  deployments/next

If device token canot be interpreted, the API can return 400 Bad Request.

Signed-off-by: Maciej Borzecki <f609d9f713abcd5f8f0e51f08dc151638a7681e7@rndity.com>

pasinskim/deployments,pasinskim/deployments,pasinskim/deployments,pasinskim/deployments