mfd: twl4030: Cleanup interrupt handling

irq_desc checking in a function which is called with that irq
descriptor locked, is pointless. Equally pointless as the irq desc
check in the interrupt service routine. The driver sets those lines
up, so that cant go away magically.

Remove the open coded handler magic and use the proper accessor.

No need to fiddle with irq_desc in the type setting function. The
original value is in irq_data and the core code stores the new setting
when the return value is 0.

This driver needs to be converted to threaded interrupts and buslock.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>