[media] docs-rst: fix some broken struct references

The :c:type: references point to the structure name, and not to
struct foo.

Fixed via this shell script:

	for i in `find Documentation/media -type f`; do perl -ne 'if (s/\:c\:type\:\`struct\s*(\S+)\`/struct :c:type:`$1`/) { s/struct\s+struct/struct/;  s/(struct\s+\:c\:type\:\`\S+\`)\s+structure/$1/;  } print $_' <$i >a && mv a $i; done

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>