pipewire: Convert confusing appends to override syntax

While in this case `RRECOMMENDS:class-target +=` wouldn't result in any
unwanted override, there is no guarantee there won't be a change, which
would be hidden by this override. To avoid any surprises in the future
let's use `:append:class-target =` syntax here.

Signed-off-by: Michal Sieron <michalwsieron@gmail.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-multimedia/recipes-multimedia/pipewire/pipewire_1.6.2.bb

@@ -282,7 +282,7 @@ FILES:${PN} = " \
     ${bindir}/pipewire-vulkan \
 "
 
-RRECOMMENDS:${PN}:class-target += " \
+RRECOMMENDS:${PN}:append:class-target = " \
 	pipewire-modules-meta \
 	pipewire-spa-plugins-meta \
 "