Simplify exec_permission_lite() logic

Instead of returning EAGAIN and having the caller do something
special for that case,  just do the special case directly.

Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>