irqchips: Replace __this_cpu_ptr uses

[ARM specific]

These are generally replaced with raw_cpu_ptr. However, in
gic_get_percpu_base() we immediately dereference the pointer. This is
equivalent to a raw_cpu_read. So use that operation there.

Cc: nicolas.pitre@linaro.org
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>