LoongArch: Check the return value when creating kobj

Add a check for the return value of kobject_create_and_add(), to ensure
that the kobj allocation succeeds for later use.

Cc: stable@vger.kernel.org
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>