net: enetc: fix check for allocation failure

This was supposed to be a check for if dma_alloc_coherent() failed
but it has a copy and paste bug so it will not work.

Fixes: fb8629e2 ("net: enetc: add support for software TSO")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/20211013080456.GC6010@kili


Signed-off-by: Jakub Kicinski <kuba@kernel.org>