media: davinci: get rid of an unused function

vpif_get_default_field() seems to be some left-over from a
past code that sets the field order.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Lad Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>