mfd: palmas: Initialise client->of_node for dummy created client

Palmas device have three different i2c addresses. The device creates
the two new dummy i2c clients for accessing the register by using
primary client adapter. This new dummy i2c client have their of_node
as NULL.

The dummy i2c client is used for registering interrupt and on this,
it creates irq domain handle. This created irq domain handle has
their of_node as NULL.

Now when any child of this device is registered through the DT as
follows:
         palmas: tps65913@58 {
         	::::::::::::::::::

         	#interrupt-cells = <2>;
                interrupt-controller;

                palmas_rtc {
                       compatible = "ti,palmas-rtc";
                       interrupt-parent = <&palmas>;
                       interrupts = <8 0>;
                };
                ::::::::::;;;
         };

And child driver (palam-rtc in this case) get their irq number as
	irq = platform_get_irq(pdev, 0);

The returned irq number is error in this case. The reason is that
the created irq_domain handle for the palmas interrupt does not have
valid node and so matching of node fails with palmas node.

Hence initialising the newly dummy created client->of_node with the
primary clients of_node so that irq_domain handle have proper of_node
for matching.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>