wcn36xx: use !! when assigning int as a boolean

bd->tx_comp is a single bit in a bitfield, so assigning
"info->flags & IEEE80211_TX_CTL_REQ_TX_STATUS" only happens
to work because TX_STATUS is defined to BIT(0); if it were
any other bit this assignment would fail.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>