The wrong bit was masked when acking langwell gpio interrupts.

Reason for maskig the wrong bit was probably because__ffs() and ffs() functions
return bit indexes differently (0..31 vs 1..32)

This fixes langwell based devices from hanging when a gpio interrupt is
triggered and undoes the breakage which occurred in change set
732063b9Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>