Check to see if the hwirq is already associated with another virq on
this IRQ domain. If so, then disassociate it before associating the
hwirq with the new virq.

This is a temporary hack that is needed in order to not break git
bisect for existing boards. The next patch in this series converts
spmi-gpio to be a hierarchical IRQ chip, then there are several patches
to update all of the device tree files, and finally this patch will be
reverted within the same patch series.

IRQs for spmi-gpio are all initially setup without an IRQ hierarchy
on pmic-arb when mfd/qcom-spmi-pmic.c is probed (via the
devm_of_platform_populate call) due to the interrupts property in
device tree. Once spmi-gpio is converted to be a hierarchical IRQ chip
in the next patch, existing users of gpio[d]_to_irq() will call
pmic_gpio_to_irq(), and that will use the new IRQ chip code in
spmi-gpio that sets up the IRQ in an IRQ hierarchy. The hwirq is now
associated with two Linux virqs and interrupts will not work as
expected. This patch corrects that issue.

Driver was tested using gpio-keys and iadc/vadc on the LG Nexus 5
(hammerhead) phone.
Signed-off-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>