[media] DocBook: Fix typo in intro.xml

This patch fix spelling typos in intro.xml.
This xml file is not created from comments within source,
I fix the xml file.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
[hans.verkuil@cisco.com: removed mention of obsolete devfs]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>