e100: replace deprecated strncpy with strscpy

e100: 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.

The "...-1" pattern makes it evident that netdev->name is expected to be
NUL-terminated.

Meanwhile, it seems NUL-padding is not required due to alloc_etherdev
zero-allocating 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.

This is in line with other uses of strscpy on netdev->name:
$ rg "strscpy\(netdev\->name.*pci.*"

drivers/net/ethernet/intel/e1000e/netdev.c
7455:   strscpy(netdev->name, pci_name(pdev), sizeof(netdev->name));

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
10839:  strscpy(netdev->name, pci_name(pdev), sizeof(netdev->name));

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>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231017190411.2199743-4-jacob.e.keller@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>