sfc: ef10: fix TX queue lookup in TX event handling

We're starting from a TXQ label, not a TXQ type, so
 efx_channel_get_tx_queue() is inappropriate.  This worked by chance,
 because labels and types currently match on EF10, but we shouldn't
 rely on that.

Fixes: 12804793 ("sfc: decouple TXQ type from label")
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>