media: davinci: variable 'common' set but not used

Get rid of those two warnings:
drivers/media/platform/davinci/vpif_capture.c: In function 'vpif_remove':
drivers/media/platform/davinci/vpif_capture.c:1722:21: warning: variable 'common' set but not used [-Wunused-but-set-variable]
  struct common_obj *common;
                     ^~~~~~
drivers/media/platform/davinci/vpif_display.c: In function 'vpif_remove':
drivers/media/platform/davinci/vpif_display.c:1342:21: warning: variable 'common' set but not used [-Wunused-but-set-variable]
  struct common_obj *common;
                     ^~~~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>