ARM: cpu topology: fix warning

kernel/sched.c:7354:2: warning: initialization from incompatible pointer type

Align cpu_coregroup_mask prototype interface with sched_domain_mask_f typedef
use int cpu instead of unsigned int cpu

Change-Id: Ifc19b964035e8bb4e153e155a67c16eec4928535
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>