net: lio_core: remove redundant assignment to variable tx_done

The variable tx_done is being assigned with a value that is never read
as the function returns a few statements later.  The assignment is
redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>