genirq/devres: Use dev_name(dev) as default for devname

Allow the devname parameter to be NULL and use dev_name(dev) in this case.
This should be an appropriate default for most use cases.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: http://lkml.kernel.org/r/05c63d67-30b4-7026-02d5-ce7fb7bc185f@gmail.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>