wifi: ath12k: fix invalid access to memory

In ath12k_dp_rx_msdu_coalesce(), rxcb is fetched from skb and bool
is_continuation is part of rxcb.
Currently, after freeing the skb, the rxcb->is_continuation accessed
again which is wrong since the memory is already freed.

This leads to following KASAN trace -
BUG: KASAN: use-after-free in ath12k_dp_rx_h_ppdu+0x18f4/0x1ab0 [ath12k].

Hence fix the issue by locally defining bool is_continuation from rxcb,
so that after freeing skb also we can use is_continuation.

Fixes: d8899132 ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Signed-off-by: Sarika Sharma <quic_sarishar@quicinc.com>
Signed-off-by: Tamizh Chelvam Raja <tamizh.raja@oss.qualcomm.com>
Signed-off-by: Raj Kumar Bhagat <quic_rajkbhag@quicinc.com>
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>