wifi: ath12k: fix undefined behavior with __fls in dp

wifi: ath12k: fix undefined behavior with __fls in dp

When max virtual ap interfaces are configured in all the bands
with ACS and hostapd restart is done every 60s,
a crash is observed at random times because of handling the
uninitialized peer fragments with fragment id of packet as 0.

"__fls" would have an undefined behavior if the argument is passed
as "0". Hence, added changes to handle the same.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Signed-off-by: Harshitha Prem <quic_hprem@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230821130343.29495-3-quic_hprem@quicinc.com