ext2: fix improper assignment for e_value_offs

In the process of changing value for existing EA,
there is an improper assignment of e_value_offs(setting to 0),
because it will be reset to incorrect value in the following
loop(shifting EA values before target). Delayed assignment
can avoid this issue.

Link: https://lore.kernel.org/r/20200603084429.25344-1-cgxu519@mykernel.net


Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Jan Kara <jack@suse.cz>