nios2: Replace strcpy() with strscpy() and simplify setup_cpuinfo()

strcpy() is deprecated; use strscpy() instead.

Since the destination buffer has a fixed length, strscpy() automatically
determines its size using sizeof() when the size argument is omitted.
This makes the explicit size argument unnecessary - remove it.

Now, combine both if-else branches using strscpy() and the same buffer
into a single statement to simplify the code.

No functional changes intended.

Link: https://github.com/KSPP/linux/issues/88


Cc: linux-hardening@vger.kernel.org
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>