Having a lock in snd_rawmidi_runtime can be a problem especially when
a substream is accessed from the outside, as the runtime creation
might be racy with the external calls.  As a first step for hardening,
move the spinlock from snd_rawmidi_runtime to snd_rawmidi_substream.

This patch just replaces the lock calls, no real functional change is
put yet.

Link: https://lore.kernel.org/r/20220617144051.18985-3-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>