MAINTAINERS: nolibc: update tree location

The nolibc tree moved out of Willys user namespace into its own.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20230916-nolibc-tree-v1-1-06c9b59a5035@weissschuh.net