pnpacpi: reduce printk severity for "pnpacpi: exceeded the max number of ..."

We have been printing these messages at KERN_ERR since 2.6.24,
per http://bugzilla.kernel.org/show_bug.cgi?id=9535

But KERN_ERR pops up on a console booted with "quiet"
and causes users to get alarmed and file bugs
about the message itself:
https://bugzilla.redhat.com/show_bug.cgi?id=436589

So reduce the severity of these messages to
KERN_WARNING, which is not printed by "quiet".

This message will still be seen without "quiet",
but a lot of messages are printed in that mode
and it will be less likely to cause undue alarm.

We could go all the way to KERN_DEBUG, but this
is a real warning after all, so it seems prudent
not to require "debug" to see it.

Signed-off-by: Len Brown <len.brown@intel.com>