libbb: add skip_dev_pfx()

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/init/init.c b/init/init.c
index 481f551..2eb8f1a 100644
--- a/init/init.c
+++ b/init/init.c
@@ -568,9 +568,7 @@
 			goto bad_entry;
 		/* turn .*TTY -> /dev/TTY */
 		if (tty[0]) {
-			if (strncmp(tty, "/dev/", 5) == 0)
-				tty += 5;
-			tty = concat_path_file("/dev/", tty);
+			tty = concat_path_file("/dev/", skip_dev_pfx(tty));
 		}
 		new_init_action(1 << action, token[3], tty);
 		if (tty[0])