irqchip: bcm7120-l2: Make sure all register accesses use base+offset

A couple of accesses to IRQEN (base+0x00) just used "base" directly, so
they would break if IRQEN ever became nonzero.  Make sure that all
reads/writes specify the register offset constant.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lkml.kernel.org/r/1415342669-30640-9-git-send-email-cernekee@gmail.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>