fs/ext2: hint about setting the filesystem size on error

Since we now request that the user sets the exact size of the ext2/3/4
filesystem, we've had quite a few users wondering what was going on when
they enable too much and the default 60M are no longer enough.

When mkfs.ext2 fails, print a hint that the user should check the size
setting.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
[Arnout: Add *** and redirect to stderr]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>