Kobject: Replace list_for_each() with list_for_each_entry().

Use the more concise list_for_each_entry(), which allows for the
deletion of the to_kobj() routine at the same time.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>