xfs: remove extra newlines from xfs messages

xfs_warn() and friends add a newline by default, but some
messages add another one.

Particularly for the failing write message below, this can
waste a lot of console real estate!

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>