kobject: fix dereference before null check on kobj

The kobj pointer is being null-checked so potentially it could be null,
however, the ktype declaration before the null check is dereferencing kobj
hence we have a potential null pointer deference. Fix this by moving the
assignment of ktype after kobj has been null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: aa30f47c ("kobject: Add support for default attribute groups to kobj_type")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>