Revert "kobject: Remove redundant checks for whether ktype is NULL"

This reverts commit 1b28cb81

.

It is reported to cause problems, so revert it for now until the root
cause can be found.

Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: 1b28cb81

 ("kobject: Remove redundant checks for whether ktype is NULL")
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Closes: https://lore.kernel.org/oe-lkp/202402071403.e302e33a-oliver.sang@intel.com
Link: https://lore.kernel.org/r/2024020849-consensus-length-6264@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>