v4l2transform: fix cdata caps leaks

The cdata structure was freed but not its caps.
It was already done in gst_v4l2_video_dec_subclass_init() and
gst_v4l2_video_enc_subclass_init().
8 jobs from v4l2-leaks in 15 minutes and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #82270
gst indent

00:00:16

passed #82269
manifest

00:00:37

 
  Build
passed #82271
build fedora x86_64

00:02:59

 
  Test
passed #82272
check fedora

00:03:30

 
  Full Builds
passed #82273
build android arm64 api28

00:02:57

passed #82275
build cerbero cross win32

00:07:31

passed #82276
build cerbero cross win64

00:07:30

passed #82274
build cerbero fedora x86_64

00:08:39