ath11k: ensure ts.flags is initialized before bit-wise or'ing in values

Currently the structure ts is not inititalized and ts.flags contains
garbage values from the stack.  This is being passed into function
ath11k_dp_tx_status_parse that bit-wise or'ing in settings into the
ts.flags field.  To avoid flags (and other fields) from containing
garbage, initialize the structure to zero before use.

Addresses-Coverity: ("Uninitialized scalar variable)"
Fixes: d5c65159 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>