wifi: ath12k: fix invalid access to memory

In the Linux kernel, the following vulnerability has been resolved: wifi: ath12k: fix invalid access to memory In ath12k_dp_rx_msdu_coalesce(), rxcb is fetched from skb and boolean 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 might lead use-after-free error. Hence, fix by locally defining bool is_continuation from rxcb, so that after freeing skb, is_continuation can be used. Compile tested only.