_desc is defined in __wil_tx_vring_tso() and may not be set in
case len is 0, verify _desc is set.
Signed-off-by: NAlexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: NMaya Erez <merez@codeaurora.org>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>