shell: mufs: add unmount command

source/shell/mufs.c

@@ -28,6 +28,7 @@ static void do_mufs_ls(const char *s);
 
 static struct cmd mufs_cmds[] = {
 	{ "mount", do_mufs_mount },
+	{ "unmount", do_mufs_unmount },
 	{ "format", do_mufs_format },
 	{ "mkdir", do_mufs_mkdir },
 	{ "rmdir", do_mufs_rmdir },