usb: device: avoid starving other threads in CDC ACM UART fifo_fill

The check for the device being configured or suspended in the fifo_fill
implementation can starve other threads, because the early return does
not change the state of the TX path, and fifo_fill is called again
from the callback loop. The ringbuffer that emulates the TX FIFO can be
filled and marked ready as long as the space is available.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>
1 file changed