ath11k: remove conversion to bool in ath11k_dp_rxdesc_mpdu_valid()

The '==' expression itself is bool, no need to convert it to bool again.
This fixes the following coccicheck warning:

drivers/net/wireless/ath/ath11k/dp_rx.c:255:46-51: WARNING: conversion
to bool not needed here

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200420123718.3384-1-yanaijie@huawei.com