selftests/bpf: Fix vfs_link kprobe definition

Since commit 6521f891 ("namei: prepare for idmapped mounts")
vfs_link's prototype was changed, the kprobe definition in
profiler selftest in turn wasn't updated. The result is that all
argument after the first are now stored in different registers. This
means that self-test has been broken ever since. Fix it by updating the
kprobe definition accordingly.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220331140949.1410056-1-nborisov@suse.com