Documentation: userspace-api/media: drop doubled words

Drop duplicated words in Documentation/userspace-api/media/.
This addresses the words "struct" and "value".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: dev-sdr.rst: there is two -> there are two]
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>