drivers: eth_nxp_enet_qos: Update as many desc as possible

Instead of looping through only the amount of descriptors there are,
maybe it is possible to get some more things received in one work item
than even the max number of descriptors if RX is processed fast enough,
instead of waiting for work to be scheduled again.

So change to go around the ring until we actually hit a DMA owned
descriptor.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>