platform/surface: tabletsw: Fix __le32 integer access

platform/surface: tabletsw: Fix __le32 integer access

The sources.count field is a __le32 inside a packed struct. So use the
proper functions to access it.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 9f794056db5b ("platform/surface: Add KIP/POS tablet-mode switch driver")
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20220717120735.2052160-1-luzmaximilian@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>