MFC r326278 (manu):

growfs: Commit the changes after expanding the partition

 This fix the problem in arm snapshot present since at least 6 months
 where growfs was failing at firstboot and dropped you in a single
 user shell.

Note: In addition to this merge, kern.geom.part.mbr.enforce_chs has
been enabled on the build machine to mitigate against the issue in
the PR referenced.

PR:		226536
Sponsored by:	The FreeBSD Foundation

etc/rc.d/growfs

@@ -89,6 +89,7 @@ growfs_start ()
 		exit 0
 	}
 }' dev="$rawdev"
+	gpart commit "$rootdev"
 	growfs -y /dev/"$rootdev"
 }