mfd: MAX77693: Fix interrupt handling bug

This patch fix bug related to interrupt handling for MAX77693 devices.
- Unmask interrupt masking bit for charger/flash/muic to revolve
that interrupt isn't happened when external connector is attached.
- Fix wrong regmap instance when muic interrupt is happened.

This patch were discussed and confirm discussion about this patch on below url:
http://lkml.org/lkml/2012/7/16/118



Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>