qca-wifi: Assign proper precac_index for legacy preCAC

Bring up a Cascade AP in HT80 mode, country DK and enable preCAC config.
During vap start, a preCAC channel is chosen by invoking
tgt_dfs_find_vht80_precac_chan_freq() and then
dfs_start_precac_timer_for_freq() is invoked to start the preCAC timer.

In dfs_start_precac_timer_for_freq(), the dfs pdev object is fetched
indexing cur_precac_dfs_index in DFS SOC object as follows:
"dfs_soc_obj->dfs_priv[dfs_soc_obj->cur_precac_dfs_index].dfs".

The cur_precac_dfs_index is initialized to 0xFF in dfs_rcac_sm_create().
This index is then over-written to the current DFS pdev index in case
of agile preCAC in dfs_prepare_agile_precac_chan() API. This API is not
invoked in case of legacy preCAC and hence cur_precac_dfs_index continues
to hold 0xFF. This leads to kernel paging request failure
and the system crashes.

Initialize 'cur_precac_dfs_index' to dfs->dfs_psoc_idx which holds
the index of the active dfs pdev.

CRs-Fixed: 2708233
Change-Id: I3aae7ea8f611d72bfe23c20cc2a34d94bba83485

umac/dfs/core/src/misc/dfs_zero_cac.c

@@ -4095,6 +4095,7 @@ void dfs_start_precac_timer_for_freq(struct wlan_dfs *dfs,
 	struct dfs_soc_priv_obj *dfs_soc_obj;
 
 	dfs_soc_obj = dfs->dfs_soc_obj;
+	dfs_soc_obj->cur_precac_dfs_index = dfs->dfs_psoc_idx;
 	dfs = dfs_soc_obj->dfs_priv[dfs_soc_obj->cur_precac_dfs_index].dfs;
 #define EXTRA_TIME_IN_SEC 5
 	dfs_soc_obj->dfs_precac_timer_running = 1;