fs/ext2: default to ext2 rev1

fs/ext2: default to ext2 rev1

Rev0 is very old (E.G. from before Linux was maintained in git), the kernel
prints a scary warning when used:

EXT4-fs warning (device sda): ext4_update_dynamic_rev:746: updating to rev 1
because of new feature flag, running e2fsck is recommended

And rev0 support is broken in u-boot 2016.11:
http://lists.denx.de/pipermail/u-boot/2016-December/275916.html

So default to rev1 instead.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>