ALSA: seq: Prohibit creating ports with special numbers

Some port numbers are special, such as 254 for subscribers and 255 for
broadcast.  Return error if application tries to create such a port.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-24-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>