Do not call 'ima_path_check()' for each path component

Not only is that a supremely timing-critical path, but it's hopefully
some day going to be lockless for the common case, and ima can't do
that.

Plus the integrity code doesn't even care about non-regular files, so it
was always a total waste of time and effort.

Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>