[gnome-control-center] subprojects: Update libgvc

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 8c84b9f0d37882c955432eb0b342e7a8fef58c74
Author: Pauli Virtanen <pav iki fi>
Date:   Sat Mar 5 18:49:07 2022 +0200

    subprojects: Update libgvc
    
    This update is necessary to fix a bug that can cause sound device
    profiles to be missing, possibly making some sound device ports
    unusable.
    
    See https://gitlab.gnome.org/GNOME/libgnome-volume-control/-/merge_requests/19
    Fixes #1668

 subprojects/gvc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/subprojects/gvc b/subprojects/gvc
index 7a621180b..8e7a5a4c3 160000
--- a/subprojects/gvc
+++ b/subprojects/gvc
@@ -1 +1 @@
-Subproject commit 7a621180b46421e356b33972e3446775a504139c
+Subproject commit 8e7a5a4c3e51007ce6579292642517e3d3eb9c50