iio: pressure: bmp280: fix runtime suspend/resume crash

In commit 3d838118 ("iio: pressure: bmp280: add power management")

For some reason the code in the runtime suspend/resume hooks
got wrong (I suspect in the ambition to cut down boilerplate)
and it seems it was tested without CONFIG_PM and crashes like
so for me:

Unable to handle kernel NULL pointer dereference at virtual address 0000000c
pgd = c0204000
[0000000c] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 1 PID: 89 Comm: kworker/1:2 Not tainted
  4.7.0-03348-g90dc3680458a-dirty #99
Hardware name: Generic DT based system
Workqueue: pm pm_runtime_work
task: df3c6300 ti: dec8a000 task.ti: dec8a000
PC is at regulator_disable+0x0/0x6c
LR is at bmp280_runtime_suspend+0x3c/0xa4

Dereferencing the BMP280 state container properly fixes the problem,
sorry for screwing up.

Fixes: 3d838118 ("iio: pressure: bmp280: add power management")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>