[ARM] 2869/1: ixp4xx: correct ioread*/iowrite*

Patch from David Vrabel

Correct the ioread* and iowrite* functions.  In particular, add an offset to the cookie in ioport_map so we can map I/O port ranges starting from 0 (0 is for reporting errors).

Signed-off-by: David Vrabel <dvrabel@arcom.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>