doc: base: Fix reference to virtual function

The hotdoc syntax is #ClassName::function, but the code was using
without anything before.

Part-of: <gstreamer/gstreamer!808>
38 jobs for !808 with basesink-doc-fix in 30 minutes and 23 seconds (queued for 3 seconds)
detached
Status Name Job ID Coverage
  Build Docker
passed alpine amd64 manifest builder docker #9689436

00:00:29

passed android docker #9689435

00:00:31

passed cerbero fedora amd64 docker #9689434

00:00:15

passed fedora amd64 docker #9689433

00:00:12

passed gst-indent amd64 docker #9689437

00:00:15

passed windows amd64 docker #9689438
windows shell 1809

00:00:09

 
  Preparation
passed check allow-edit #9689441

00:00:10

passed gst indent #9689440

00:00:06

passed manifest #9689439

00:00:22

 
  Build
passed build cerbero cross-android universal #9689450
gstreamer

00:12:40

passed build cerbero cross-ios universal #9689454
gst-ios-14.3

00:19:34

passed build cerbero cross win32 #9689451
gstreamer

00:09:13

passed build cerbero cross win64 #9689452
gstreamer

00:09:14

passed build cerbero fedora x86_64 #9689449
gstreamer

00:08:50

passed build cerbero macos x86_64 #9689453
gst-macos-11.1

00:10:24

passed build cerbero msvc x86_64 #9689455
docker windows gstreamer-windows 1809

00:12:56

passed build clang fedora x86_64 #9689445

00:11:52

manual build msys2 #9689448
docker windows 1809 allowed to fail manual
passed build nodebug fedora x86_64 #9689442

00:11:15

passed build static fedora x86_64 #9689443

00:11:00

passed build static nodebug fedora x86_64 #9689444

00:10:55

passed build vs2017 amd64 #9689446
docker windows 1809

00:13:32

passed build vs2017 x86 #9689447
docker windows 1809

00:13:49

 
  Test
passed check fedora #9706624
gstreamer

00:05:16

passed integration testsuites fedora 1/4 #9689457
gstreamer

00:09:23

passed integration testsuites fedora 2/4 #9689458
gstreamer

00:09:13

passed integration testsuites fedora 3/4 #9689459
gstreamer

00:09:18

passed integration testsuites fedora 4/4 #9689460
gstreamer

00:10:18

passed valgrind bad #9689465
gstreamer

00:05:19

passed valgrind base #9689462
gstreamer

00:09:30

passed valgrind core #9689461
gstreamer

00:07:58

passed valgrind ges #9689466
gstreamer

00:10:15

passed valgrind good #9689463
gstreamer

00:09:34

passed valgrind ugly #9689464
gstreamer

00:03:55

failed check fedora #9689456
gstreamer

00:10:33

 
  Integrate
passed cross-android universal examples #9689467

00:06:35

passed cross-ios universal examples #9689469
gst-ios-14.3

00:04:35

passed documentation #9689468

00:13:55