[PATCH] Change log level of a message of acpi_memhotplug to KERN_DEBUG

I suppose this message seems quite useless except debugging.  It just shows
"Hotplug Mem Device".  System admin can't know anything by this message.
So, I would like to change it to KERN_DEBUG.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>