ASoC: rsnd: spin lock for interrupt handler

ASoC: rsnd: spin lock for interrupt handler

Renesas R-Car driver interrupt handler was not locked before.
But now, SSI/SRC interrupt handler calls restart function
which should be called under spin lock.
Below error might happen witout this patch.

Unable to handle kernel NULL pointer dereference at virtual address 00000048
pgd = edfac000
[00000048] *pgd=6e0f0831, *pte=00000000, *ppte=00000000
Internal error: Oops: 17 [#1] SMP ARM
CPU: 0 PID: 2009 Comm: aplay Not tainted 4.1.0-rc2-dirty #4
Hardware name: Generic R8A7790 (Flattened Device Tree)
task: eeac9040 ti: eebe8000 task.ti: eebe8000
PC is at rsnd_get_adinr+0x28/0x60
LR is at rsnd_src_ssiu_start+0xdc/0x19c
pc : [<c0409790>]    lr : [<c040c068>]    psr: a0000193
sp : eebe9e58  ip : eebe9e68  fp : eebe9e64
r10: c06ed9d0  r9 : ee919d10  r8 : 00000001
r7 : 00000001  r6 : ee1cb090  r5 : 00000000  r4 : edcaa418
r3 : 00000000  r2 : eea8ce00  r1 : 80000193  r0 : edcaa418
...

Reported-by: Cao Minh Hiep <cm-hiep@jinso.co.jp>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Tested by: Cao Minh Hiep <cm-hiep@jinso.co.jp>
Signed-off-by: Mark Brown <broonie@kernel.org>