videodecoder: fix documentation

Fix list indentation, othewise it is interpreted as verbatim.
29 jobs for master in 30 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #2008351
gst indent

00:00:30

manual #2008350
manual
manifest
 
  Build
created #2008361
gstreamer
build cerbero cross-android universal
created #2008365
gst-ios-13.2
build cerbero cross-ios universal
created #2008362
gstreamer
build cerbero cross win32
created #2008363
gstreamer
build cerbero cross win64
created #2008360
gstreamer
build cerbero fedora x86_64
created #2008364
gst-macos-10.15
build cerbero macos x86_64
created #2008356
build clang fedora x86_64
created #2008352
build fedora x86_64
created #2008359
docker windows 1809
build msys2
created #2008353
build nodebug fedora x86_64
created #2008354
build static fedora x86_64
created #2008355
build static nodebug fedora x86_64
created #2008357
docker windows 1809
build vs2017 amd64
created #2008358
docker windows 1809
build vs2017 x86
 
  Test
created #2008366
gstreamer
check fedora
created #2008367
gstreamer
integration testsuites fedora 1/4
created #2008368
gstreamer
integration testsuites fedora 2/4
created #2008369
gstreamer
integration testsuites fedora 3/4
created #2008370
gstreamer
integration testsuites fedora 4/4
created #2008374
gstreamer
valgrind bad
created #2008371
gstreamer
valgrind base
created #2008375
gstreamer
valgrind ges
created #2008372
gstreamer
valgrind good
created #2008373
gstreamer
valgrind ugly
 
  Integrate
created #2008376
cross-android universal examples
created #2008378
gst-ios-13.2
cross-ios universal examples
created #2008377
documentation