xfs_quota: fix up dump and report documentation

xfs_quota: fix up dump and report documentation

Documentation for these commands was a bit of a mess.

1) The help args were respecified in the _help() functions, overwriting
   the strings which had been set up in the _init functions as all
   other commands do. Worse, in the report case, they differed.

2) The -L/-U dump options were not present in either short help string.

3) The -L/-U dump options were not documented in the xfs_quota manpage.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>