perf: Fix prototype of find_pmu_context()

perf: Fix prototype of find_pmu_context()

For some reason find_pmu_context() is defined as returning void * rather
than a __percpu struct perf_cpu_context *. As all the requisite types are
defined in advance there's no reason to keep it that way.

This patch modifies the prototype of pmu_find_context to return a
__percpu struct perf_cpu_context *.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1392054264-23570-2-git-send-email-mark.rutland@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>