[media] am437x: remove unused variable

drivers/media/platform/am437x/am437x-vpfe.c: In function 'vpfe_get_subdev_input_index':
drivers/media/platform/am437x/am437x-vpfe.c:1679:27: warning: variable 'sdinfo' set but not used [-Wunused-but-set-variable]
  struct vpfe_subdev_info *sdinfo;
                           ^

Cc: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>