atheros: fix return value check in atl1_tso()

in atl1_tso(), it should check the return value of pskb_trim(),
and return an error code if an unexpected value is returned
by pskb_trim().

Fixes: 401c0aab

 ("atl1: simplify tx packet descriptor")
Signed-off-by: Yuanjun Gong <ruc_gongyuanjun@163.com>
Link: https://lore.kernel.org/r/20230722142511.12448-1-ruc_gongyuanjun@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>