bus: arm-ccn: Fix XP watchpoint settings bitmask

The code setting XP watchpoint comparator and mask registers should, in
order to be fully compliant with specification, zero one or more most
significant bits of each field. In both L cases it means zeroing bit 63.
The bitmask doing this was wrong, though, zeroing bit 60 instead.
Fortunately, due to a lucky coincidence, this turned out to be fairly
innocent with the existing hardware.

Fixed now.

Cc: stable@vger.kernel.org # 3.17+
Signed-off-by: Pawel Moll <pawel.moll@arm.com>