ARM: mach-shmobile: armadillo800eva: Fix GPIO buttons descriptions

The GPIO buttons are named SW3, SW4, SW5 and SW6 on the board
silkscreen. Update the buttons descriptions accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>