fdkaac: Syntax tweaks to increase readability

Mostly move some assignments out of conditionals that gst-indent
completely destroys.
6 jobs for fdkaac-modes in 34 minutes and 34 seconds (queued for 65 minutes and 26 seconds)
Status Job ID Name Coverage
  Preparation
passed #65400
gst indent

00:00:33

passed #65399
manifest

00:00:19

 
  Build
passed #65401
build fedora x86_64

00:03:32

 
  Test
passed #65402
check fedora

00:15:42

 
  Full Builds
passed #65403
build android arm64 api28

00:02:22

passed #65404
build cerbero fedora x86_64

00:12:03