HID: magicmouse: fix kerneldoc for struct magicmouse_sc

Description for hdev, work and battery_timer of struct magicmouse_sc were
missing. Fix that.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312261056.AmFPDIL5-lkp@intel.com/


Signed-off-by: Jiri Kosina <jkosina@suse.com>