ALSA: pcmtest: Replace deprecated strcpy with strscpy_pad in setup_patt_bufs

ALSA: pcmtest: Replace deprecated strcpy with strscpy_pad in setup_patt_bufs

strcpy() has been deprecated [1] because it performs no bounds checking
on the destination buffer, which can lead to buffer overflows. Replace
it with the safer strscpy_pad(), and use kmalloc() instead of kzalloc()
because strscpy_pad() zero-pads the destination buffer and therefore
avoids writing to it twice.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20251119135217.233084-1-thorsten.blum@linux.dev
Signed-off-by: Takashi Iwai <tiwai@suse.de>