ext4-new-features: modify ext4_get_inode_version.sh not know $EXT4_DEV definition

ext4_get_inode_version.sh use $EXT4_DEV, but it really doesn't know what is $EXT4_DEV.
That cause other cases which use ext4_get_inode_version.sh to fail.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>