staging: bcm2835-camera: Set the field value within each buffer

Fixes a v4l2-compliance failure
v4l2-test-buffers.cpp(415): g_field() == V4L2_FIELD_ANY

The driver only ever produces progresive frames, so field should
always be set to V4L2_FIELD_NONE.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>