MFD: twl6040: Demand valid interrupt configuration

In order to operate correctly twl6040 needs correct
interrupt configuration.
The slave drivers (vibra, and ASoC codec) will refuse
to probe, if the interrupt configuration is not correct.
In this way some checks can be removed from the code.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>