xfs: don't zero structure members after a memset(0)

Commit 408cc4e9
added memset(0, ...) to allocation args structures,
so there is no need to explicitly set any of the fields
to 0 after that.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>