Fix Documentation/filesystems/ramfs-rootfs-initramfs.txt

First a file hello.c is created, then the file hello2.c is compiled.
Change this to hello.c

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Signed-off-by: Rob Landley <rob@landley.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>