xfs: cleanup duplicate initializations

follow these guidelines:
- leave initialization in the declaration block if it fits the line
- move to the code where it's more suitable ('for' init block)

The last chunk was modified from David's original to be a correct
fix for what appeared to be a duplicate initialization.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>