firmware/psci: fix application of sizeof to pointer

sizeof when applied to a pointer typed expression gives the size of
the pointer.

./drivers/firmware/psci/psci_checker.c:158:41-47: ERROR application of sizeof to pointer

This issue was detected with the help of Coccinelle.

Fixes: 7401056d ("drivers/firmware: psci_checker: stash and use topology_core_cpumask for hotplug tests")
Cc: stable@vger.kernel.org
Reported-by: Zeal Robot <zealci@zte.com.cn>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: jing yangyang <jing.yangyang@zte.com.cn>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>