ALSA: jack: Improve string handling in jack_kctl_name_gen

ALSA: jack: Improve string handling in jack_kctl_name_gen

If appending " Jack" is not necessary, replace snprintf("%s", ...) with
the faster strscpy().

Additionally, rename 'need_cat' to the clearer 'append_suf', use local
variables for the suffix and its length, remove the confusing comment,
compare strncmp() to 0, and use 'size_t' for the 'size' function
parameter.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20260125155159.98720-1-thorsten.blum@linux.dev
Signed-off-by: Takashi Iwai <tiwai@suse.de>