mfd: tps65090: Don't tell child devices we have an IRQ if we don't

If we weren't given an interrupt we shouldn't tell child devices (like
the tps65090 charger) that they have an interrupt.  This is needed so
that we can support polling mode in the tps65090 charger driver.

See also (charger: tps65090: Allow charger module to be used when no
irq).

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>