V4L/DVB (11454): gspca - m5602-mt9m111: Remove the unused power_down struct member

The power_down sensor struct member is almost has no purpose in the current driver abstraction. Remove it.

Signed-off-by: Erik Andr?n <erik.andren@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>