coreaudio: swap Surround with RearSurround when needed

Tested on macOS 12.5, compared with the same vlc/sample/amplifier on
Windows.

Surround and RearSurround are indeed swapped for 7.1, same for tvOS (cf.
next).

But why ?

(cherry picked from commit 0a65098f)
Signed-off-by: Thomas Guillem <thomas@gllm.fr>