Give a error when running out of iomem areas.

The limit of iomem areas is quite low. Without the
debug print, it is quite hard to figure out why more
devices are not getting registered.

Signed-off-by: Riku Voipio <riku.voipio@nokia.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
