x86/resctrl: Fix kfree() of the wrong type in domain_add_cpu()

x86/resctrl: Fix kfree() of the wrong type in domain_add_cpu()

Commit in Fixes separated the architecture specific and filesystem parts
of the resctrl domain structures.

This left the error paths in domain_add_cpu() kfree()ing the memory with
the wrong type.

This will cause a problem if someone adds a new member to struct
rdt_hw_domain meaning d_resctrl is no longer the first member.

Fixes: e4768d23c57b ("x86/resctrl: Split struct rdt_domain")
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lkml.kernel.org/r/20210917165924.28254-1-james.morse@arm.com