ASOC: dsp: add spin_lock for q6asm_add_hdr

During SSR, ac could get freed after unlock the session lock
during the execution of q6asm_callback. If we try to get the
ac->cmd_lock after ac freed, kernel panic happens.
Remove mutex_lock in reset_event to avoid kernel panic.
Add spin_lock_irqsave in q6asm_add_hdr and change spin_lock to
spin_lock_irqsave in q6asm_callback to add synchronize between
q6asm_add_hdr and q6asm_callback to avoid kernel panic.

Change-Id: I72cf959fe6a764920a13d565c72243a80ac4f236
Signed-off-by: Meng Wang <mengw@codeaurora.org>