rtp: fix g-i warnings

Use same variable name in function declaration as in function
definition and gtk-doc/g-i blurb.
6 jobs for rtp-meta-fix-gi-warnings in 30 minutes and 12 seconds (queued for 3 minutes and 5 seconds)
Status Job ID Name Coverage
  Preparation
passed #64750
gst indent

00:00:36

passed #64749
manifest

00:00:23

 
  Build
passed #64751
build fedora x86_64

00:03:44

 
  Test
passed #64752
check fedora

00:15:47

 
  Full Builds
passed #64753
build android arm64 api28

00:03:03

passed #64754
build cerbero fedora x86_64

00:09:39