gpio: fix test on unsigned in lnw_irq_type()

The wrong test was used, gpio is unsigned and it had an off-by-one.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: 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>