FROMGIT: binder: fix BUG_ON found by selinux-testsuite

The selinux-testsuite found an issue resulting in a BUG_ON()
where a conditional relied on a size_t going negative when
checking the validity of a buffer offset.

(cherry picked from commit 5997da82145bb7c9a56d834894cb81f81f219344
 git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git


 char-misc-linus)
Bug: 67668716
Change-Id: Ib3b408717141deadddcb6b95ad98c0b97d9d98ea
Fixes: 7a67a39320df ("binder: add function to copy binder object from buffer")
Reported-by: Paul Moore <paul@paul-moore.com>
Tested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Todd Kjos <tkjos@google.com>