kernel/kallsyms.c: fix double return

Commit 6dd06c9f ("module: make
module_address_lookup safe") introduced double returns in the function
kallsyms_lookup(), it's weird.  The second one should be removed.

Signed-off-by: WANG Cong <wangcong@zeuux.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>