mm/memory_hotplug.c: change normal message to use pr_debug

mm/memory_hotplug.c: change normal message to use pr_debug

During early boot-up, iomem_resource is set up from the boot descriptor
table, such as EFI Memory Table and e820.  Later, acpi_memory_device_add()
calls add_memory() for each ACPI memory device object as it enumerates
ACPI namespace.  This add_memory() call is expected to fail in
register_memory_resource() at boot since iomem_resource has been set up
from EFI/e820.  As a result, add_memory() returns -EEXIST, which
acpi_memory_device_add() handles as the normal case.

This scheme works fine, but the following error message is
logged for every ACPI memory device object during boot-up.

  "System RAM resource %pR cannot be added\n"

This patch changes register_memory_resource() to use pr_debug() for the
message as it shows up under the normal case.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>