ath11k: delete a stray unlock in ath11k_dbg_htt_stats_req()

The callers unlock this lock so this error path has a double unlock.

Fixes: d5c65159 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>