wifi: brcm80211: replace deprecated strncpy with strscpy

Let's move away from using strncpy and instead favor a less ambiguous
and more robust interface.

For ifp->ndev->name, we expect ifp->ndev->name to be NUL-terminated based
on its use in format strings within core.c:
67 |       char *brcmf_ifname(struct brcmf_if *ifp)
68 |       {
69 |            if (!ifp)
70 |                    return "<if_null>";
71 |
72 |            if (ifp->ndev)
73 |                    return ifp->ndev->name;
74 |
75 |            return "<if_none>";
76 |       }
...
288 |       static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
289 |                                              struct net_device *ndev) {
...
330 |       brcmf_dbg(INFO, "%s: insufficient headroom (%d)\n",
331 |                 brcmf_ifname(ifp), head_delta);
...
336 |       bphy_err(drvr, "%s: failed to expand headroom\n",
337 |                brcmf_ifname(ifp));

For di->name, we expect di->name to be NUL-terminated based on its usage
with format strings:
|       brcms_dbg_dma(di->core,
|                     "%s: DMA64 tx doesn't have AE set\n",
|                     di->name);

Looking at its allocation we can see that it is already zero-allocated
which means NUL-padding is not required:
|       di = kzalloc(sizeof(struct dma_info), GFP_ATOMIC);

For wlc->modulecb[i].name, we expect each name in wlc->modulecb to be
NUL-terminated based on their usage with strcmp():
|       if (!strcmp(wlc->modulecb[i].name, name) &&

NUL-padding is not required as wlc is zero-allocated in:
brcms_c_attach_malloc() ->
|       wlc = kzalloc(sizeof(struct brcms_c_info), GFP_ATOMIC);

For all these cases, a suitable replacement is `strscpy` due to the fact
that it guarantees NUL-termination on the destination buffer without
unnecessarily NUL-padding.

Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231017-strncpy-drivers-net-wireless-broadcom-brcm80211-brcmfmac-cfg80211-c-v3-1-af780d74ae38@google.com