xfs: don't reset the "inode core" in xfs_iread

We have the exact same memset in xfs_inode_alloc, which is always called
just before xfs_iread.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>