Resolve kernel panic that occurs on callback from sysctl when setting
hw.ciss.expose_hidden_physical=1 on a HP ProLiant DL360 G6 (and possibly
others) due to mishandling of error value in acpica on stable/7

Note that this is a direct commit as this code has been fixed in stable/8
(8.4 included) and higher release for quite some time.

PR: kern/152250
Submitted by: Loic Pefferkorn <loic-freebsd@loicp.eu>
Reviewed by: avg@