net: stmmac: clean up impossible condition

This code works but it has a static checker warning:

    drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:1687 init_dma_rx_desc_rings()
    warn: always true condition '(queue >= 0) => (0-u32max >= 0)'

Obviously, it makes no sense to check if an unsigned int is >= 0.  What
prevents this code from being a forever loop is that later there is a
separate check for if (queue == 0).

The "queue" variable is less than MTL_MAX_RX_QUEUES (8) so it can easily
fit in an int type.  Any larger value for "queue" would lead to an array
overflow when we assign "rx_q = &priv->rx_queue[queue]".

Fixes: de0b90e5

 ("net: stmmac: rearrange RX and TX desc init into per-queue basis")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220316083744.GB30941@kili
Signed-off-by: Paolo Abeni <pabeni@redhat.com>