regulator: da9210: fix lockdep warning

Commit 70cfef26 ("regulator: Add lockdep asserts to help detecting
locking misuse") successfully created this WARN, let's fix it:

[    1.218660] WARNING: CPU: 0 PID: 553 at drivers/regulator/core.c:3646 regulator_notifier_call_chain+0x5c/0x88()
...
[    1.220278] [<c0246c20>] (regulator_notifier_call_chain) from [<c02498b4>] (da9210_irq_handler+0x74/0x10c)
[    1.220412]  r7:c0080cac r6:eb1daa00 r5:e64bbf10 r4:00000002
[    1.220547] [<c0249840>] (da9210_irq_handler) from [<c0080cd8>] (irq_thread_fn+0x2c/0x44)
...

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Mark Brown <broonie@kernel.org>