mfd: tps65218: Make INT[12] and STATUS registers volatile

STATUS register can be modified by the HW, so we
should bypass cache because of that.

In the case of INT[12] registers, they are the ones
that actually clear the IRQ source at the time they
are read. If we rely on the cache for them, we will
never be able to clear the interrupt, which will cause
our IRQ line to be disabled due to IRQ throttling.

Fixes: 44b4dc61 mfd: tps65218: Add driver for the TPS65218 PMIC
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>