percpu: make pcpu_build_alloc_info() clear static buffers

pcpu_build_alloc_info() may be called multiple times when percpu is
falling back to different first chunk allocator.  Make it clear static
buffers so that they don't contain values from previous runs.

Signed-off-by: Tejun Heo <tj@kernel.org>

mm/percpu.c

@@ -1347,6 +1347,10 @@ struct pcpu_alloc_info * __init pcpu_build_alloc_info(
 	struct pcpu_alloc_info *ai;
 	unsigned int *cpu_map;
 
+	/* this function may be called multiple times */
+	memset(group_map, 0, sizeof(group_map));
+	memset(group_cnt, 0, sizeof(group_map));
+
 	/*
 	 * Determine min_unit_size, alloc_size and max_upa such that
 	 * alloc_size is multiple of atom_size and is the smallest