idevicebackup2: add cast to silence compiler warning
idevicebackup2: add cast to silence compiler warning

libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice,upbit/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice,Tatsh/libimobiledevice,Tatsh/libimobiledevice,patweb/libimobiledevice,kalev/libimobiledevice,upbit/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice/libimobiledevice,patweb/libimobiledevice,kalev/libimobiledevice,patweb/libimobiledevice,upbit/libimobiledevice,kalev/libimobiledevice