omap3: pandora: update gpio-keys data

Update gpio-keys setup so it matches what is on default firmware.
Also make use of debounce feature in gpio-keys instead of setting it
explicitly, as gpio-keys is now capable of using hardware debounce on
OMAPs thanks to recent gpiolib changes.
Also fix a sparce warning along the way.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>