ALSA: seq: Avoid confusion of aligned read size

Currently the read event packet size in snd_seq_read() is defined by
client->midi_version value that is guaranteed to be zero if UMP isn't
enabled.  But the static analyzer doesn't know of the fact, and it
still suspects as if it were leading to a potential overflow.

Add the more explicit check of CONFIG_SND_SEQ_UMP to determine the
aligned_size value for avoiding the confusion.

Fixes: 46397622

 ("ALSA: seq: Add UMP support")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/r/202305261415.NY0vapZK-lkp@intel.com/
Link: https://lore.kernel.org/r/20230605144758.6677-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>