Fix selinux denials for usbd

auditd  : type=1400 audit(0.0:9): avc: denied { dac_override } for comm="usbd" capability=1 scontext=u:r:usbd:s0 tcontext=u:r:usbd:s0 tclass=capability permissive=
auditd  : type=1400 audit(0.0:9): avc: denied { dac_override } for comm="usbd" capability=1 scontext=u:r:usbd:s0 tcontext=u:r:usbd:s0 tclass=capability permissive=0

Bug: 72397740
Test: booted the device to make sure that the denials are no longer
seen.
Change-Id: Ie276103ba261fd762fb8c24234904e3f3ce3d2f1
diff --git a/usbd/usbd.rc b/usbd/usbd.rc
index c7838e8..809044a 100644
--- a/usbd/usbd.rc
+++ b/usbd/usbd.rc
@@ -2,4 +2,4 @@
     class late_start
     oneshot
     user root
-    group root usb
+    group root usb system