gpio: Langwell GPIO driver bugfixes

- Remove wrong and unnecessary unmask operation

- Remove extra GEDR reading

This fixes the loss of interrupts which occurs when two or more pins are
triggered in close succession.

Signed-off-by: Alek Du <alek.du@intel.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>