ALSA: seq: Remove superfluous irqsave flags

spin_lock_irqsave() is used unnecessarily in various places in
sequencer core code although it's pretty obvious that the context is
sleepable.  Remove irqsave and use the plain spin_lock_irq() in such
places for simplicity.

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