media: Add V4L2_TYPE_IS_CAPTURE helper

It's all too easy to get confused by the V4L2_TYPE_IS_OUTPUT
macro, when it's used as !V4L2_TYPE_IS_OUTPUT.

Reduce the risk of confusion with macro to explicitly
check for the CAPTURE queue type case.

This change does not affect functionality, and it's
only intended to make the code more readable.

Suggested-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: checkpatch: align with parenthesis]
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>