acpi_pad: "processor_aggregator" name too long

cpi_device_class can only be 19 characters and a NULL terminator.

With the current name we get a buffer overflow in acpi_pad_add()
	strcpy(acpi_device_class(device), ACPI_PROCESSOR_AGGREGATOR_CLASS);

[akpm@linux-foundation.org: call it acpi_pad, per Shaohua Li]
Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: walter harms <wharms@bfs.de>
Acked-by: Shaohua Li <shaohua.li@intel.com>
Cc: Len Brown <lenb@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>