octeontx2-af: replace deprecated strncpy with strscpy

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We can see that linfo->lmac_type is expected to be NUL-terminated based
on the `... - 1`'s present in the current code. Presumably making room
for a NUL-byte at the end of the buffer.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Let's also prefer the more idiomatic strscpy usage of (dest, src,
sizeof(dest)) rather than (dest, src, SOME_LEN).

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231010-strncpy-drivers-net-ethernet-marvell-octeontx2-af-cgx-c-v1-1-a443e18f9de8@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/octeontx2/af/cgx.c

@@ -1218,8 +1218,6 @@ static inline void link_status_user_format(u64 lstat,
 					   struct cgx_link_user_info *linfo,
 					   struct cgx *cgx, u8 lmac_id)
 {
-	const char *lmac_string;
-
 	linfo->link_up = FIELD_GET(RESP_LINKSTAT_UP, lstat);
 	linfo->full_duplex = FIELD_GET(RESP_LINKSTAT_FDUPLEX, lstat);
 	linfo->speed = cgx_speed_mbps[FIELD_GET(RESP_LINKSTAT_SPEED, lstat)];
@@ -1230,12 +1228,12 @@ static inline void link_status_user_format(u64 lstat,
 	if (linfo->lmac_type_id >= LMAC_MODE_MAX) {
 		dev_err(&cgx->pdev->dev, "Unknown lmac_type_id %d reported by firmware on cgx port%d:%d",
 			linfo->lmac_type_id, cgx->cgx_id, lmac_id);
-		strncpy(linfo->lmac_type, "Unknown", LMACTYPE_STR_LEN - 1);
+		strscpy(linfo->lmac_type, "Unknown", sizeof(linfo->lmac_type));
 		return;
 	}
 
-	lmac_string = cgx_lmactype_string[linfo->lmac_type_id];
-	strncpy(linfo->lmac_type, lmac_string, LMACTYPE_STR_LEN - 1);
+	strscpy(linfo->lmac_type, cgx_lmactype_string[linfo->lmac_type_id],
+		sizeof(linfo->lmac_type));
 }
 
 /* Hardware event handlers */