xfs: remove shadow variable in xfs_btree_lshift

Sparse warns about a shadow variable in this function after the
Fixed: commit added another int i; with larger scope.  It's safe
to remove the one with the smaller scope to fix this shadow,
although the shadow itself is harmless.

Fixes: 2c813ad6 ("xfs: support btrees with overlapping intervals for keys")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>