r8169: remove not needed check in rtl8169_start_xmit

In rtl_tx() the released descriptors are zero'ed by
rtl8169_unmap_tx_skb(). And in the beginning of rtl8169_start_xmit()
we check that enough descriptors are free, therefore there's no way
the DescOwn bit can be set here.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/6965d665-6c50-90c5-70e6-0bb335d4ea47@gmail.com


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