mfd: tps6586x: Fix OF node refcount

mfd: tps6586x: Fix OF node refcount

Platform devices created with platform_device_alloc() call
platform_device_release() when the last reference to the device's
kobject is dropped. This function calls of_node_put() unconditionally.
This works fine for devices created with platform_device_register_full()
but users of the split approach (platform_device_alloc() +
platform_device_add()) must bump the reference of the of_node they
assign manually. Add the missing call to of_node_get().

Cc: stable@vger.kernel.org
Fixes: 62f6b0879304 ("tps6586x: Add device tree support")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260521-pdev-fwnode-ref-v1-1-88c324a1b8d2@oss.qualcomm.com
Signed-off-by: Lee Jones <lee@kernel.org>