splice07: Whitelist /proc/self/maps on pipe write

Just like with /dev/zero, splicing /proc/self/maps to writable pipe
is expected to pass. After generic splice() read emulation was removed,
it was reimplemented in commit b0072734ffaa ("tty, proc, kernfs, random:
Use copy_splice_read()")

Link: https://lore.kernel.org/ltp/20240129104327.10639-1-mdoucha@suse.cz/
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Martin Doucha <mdoucha@suse.cz>

Author: mdoucha

testcases/kernel/syscalls/splice/splice07.c

@@ -40,6 +40,7 @@ static void check_splice(struct tst_fd *fd_in, struct tst_fd *fd_out)
 		/* While these combinations succeeed */
 		case TST_FD_DEV_ZERO:
 		case TST_FD_FILE:
+		case TST_FD_PROC_MAPS:
 		case TST_FD_MEMFD:
 			return;
 		/* And this complains about socket not being connected */