rsi: Remove internal header from Tx status skb

Device specific descriptor for each TX packet is prepared on top of
skb data address. This descriptor should be pulled out before
indicating the TX status to mac80211.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>