[ARM] pxa: fix typo in BANK_OFF() macro in gpio.h

The typo was originally fixed by Mike Rapoport and missed. And is
later reported by Matthias Meier.

Signed-off-by: Matthias Meier <matthias.j.meier@gmx.net>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.miao@marvell.com>