[ARM] pxa/raumfeld: fix button name

"on/off button" was recently renamed to remove the slash character.
Follow that change in the pin polarity detection as well.

While at it, fix another cosmetic coding style flaw as well.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>