ALSA: seq: Align temporary re-locking with irqsave version

In a few places in sequencer core, we temporarily unlock / re-lock the
pool spin lock while waiting for the allocation in the blocking mode.
There spin_unlock_irq() / spin_lock_irq() pairs are called while
initially spin_lock_irqsave() is used (and spin_lock_irqrestore() at
the end of the function again).  This is likely OK for now, but it's a
bit confusing and error-prone.

This patch replaces these temporary relocking lines with the irqsave
variant to make the lock/unlock sequence more consistently.

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