stmmac: fix TX normal DESC

This patch fixs a regression raised when test on chips that use
the normal descriptor layout. In fact, no len bits were set for
the TDES1 and no OWN bit inside the TDES0.

Signed-off-by: Giuseppe CAVALLARO <peppe.cavallaro@st.com>
Tested-by: Andreas Färber <afaerber@suse.de>
Cc: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>