[ALSA] Change seq_midi.c so client name is card, rather than port, specific

Change snd_seq_midisynth_register_port() in seq_midi.c so that if a new client
is created, the client name string is based on card->shortname not
(port-specific) info->name.

Signed-off-by: Alan Horstmann <gineera@aspect135.co.uk>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>