media: v4l2-ctrl: Fix flags field on Control events

VIDIOC_DQEVENT and VIDIOC_QUERY_EXT_CTRL should give the same output for
the control flags field.

This patch creates a new function user_flags(), that calculates the user
exported flags value (which is different than the kernel internal flags
structure). This function is then used by all the code that exports the
internal flags to userspace.

Reported-by: Dimitrios Katsaros <patcherwork@gmail.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v3.17 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>