platform/x86: apple-gmux: use resource_size() with res

This should be (res->end - res->start + 1) here actually,
use resource_size() derectly.

Signed-off-by: Wang Qing <wangqing@vivo.com>
Link: https://lore.kernel.org/r/1639484316-75873-1-git-send-email-wangqing@vivo.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>