CVE-2024-41071 wifi: mac80211: Avoid address calculations via out of bounds array indexing

In the Linux kernel, the following vulnerability has been resolved:

wifi: mac80211: Avoid address calculations via out of bounds array indexing

req->n_channels must be set before req->channels[] can be used.

This patch fixes one of the issues encountered in [1].

[ 83.964255] UBSAN: array-index-out-of-bounds in net/mac80211/scan.c:364:4
[ 83.964258] index 0 is out of range for type ‘struct ieee80211_channel *[]’
[…]
[ 83.964264] Call Trace:
[ 83.964267] <TASK>
[ 83.964269] dump_stack_lvl+0x3f/0xc0
[ 83.964274] __ubsan_handle_out_of_bounds+0xec/0x110
[ 83.964278] ieee80211_prep_hw_scan+0x2db/0x4b0
[ 83.964281] __ieee80211_start_scan+0x601/0x990
[ 83.964291] nl80211_trigger_scan+0x874/0x980
[ 83.964295] genl_family_rcv_msg_doit+0xe8/0x160
[ 83.964298] genl_rcv_msg+0x240/0x270
[…]

[1] https://bugzilla.kernel.org/show_bug.cgi?id=218810