xfs: fix xfs_btree_query_range callers to initialize btree rec fully

Use struct initializers to ensure that the xfs_btree_irecs passed into
the query_range function are completely initialized.  No functional
changes, just closing some sloppy hygiene.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>