net: mvpp2: replace deprecated strncpy with strscpy

net: mvpp2: 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 expect `irqname` to be NUL-terminated based on its use with
of_irq_get_byname() -> of_property_match_string() wherein it is used
with a format string and a `strcmp`:
|       pr_debug("comparing %s with %s\n", string, p);
|       if (strcmp(string, p) == 0)
|               return i; /* Found it; return index */

NUL-padding is not required as is evident by other assignments to
`irqname` which do not NUL-pad:
|       if (port->flags & MVPP2_F_DT_COMPAT)
|               snprintf(irqname, sizeof(irqname), "tx-cpu%d", i);
|       else
|               snprintf(irqname, sizeof(irqname), "hif%d", i);

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.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
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-mvpp2-mvpp2_main-c-v1-1-51be96ad0324@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>