jack: use correct port names in 50-jack.conf

jack: use correct port names in 50-jack.conf

Change port names in 50-jack.conf from "alsa_pcm" to "system".

JACK1 v0.125.0 still provides alsa_pcm:playback_* and alsa_pcm:capture_*
port names, but only as aliases:
$ jack_lsp -A
system:capture_1
   alsa_pcm:capture_1
system:capture_2
   alsa_pcm:capture_2
system:playback_1
   alsa_pcm:playback_1
system:playback_2
   alsa_pcm:playback_2

JACK2 v1.9.12 doesn't support alsa_pcm:playback_* and alsa_pcm:capture_*
aliases anymore, so 50-jack.conf will fail for JACK2 users:
$ jack_lsp -A
system:capture_1
   alsa_pcm:hw:0:out1
system:capture_2
   alsa_pcm:hw:0:out2
system:playback_1
   alsa_pcm:hw:0:in1
system:playback_2
   alsa_pcm:hw:0:in2

As you see in both cases system:playback_* and system:capture_* are
correct port names.

Signed-off-by: Alex Ivanov <gnidorah@ya.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>