perf: Convert kmalloc_node(...GFP_ZERO...) to kzalloc_node()

Use the convenience function instead of __GFP_ZERO.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/f58599ae1a8d7b32d37e9cf283e95fba6452f7f6.1377809875.git.joe@perches.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>