devcgroup: skip superfluous checks when found the DEV_ALL elem

While walking through the whitelist, if the DEV_ALL item is found, no more
check is needed.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>