gfs2: kerneldoc warning fixes

Fixes the following kernel-doc warnings:
Warning(fs/gfs2/aops.c:180): No description found for parameter 'wbc'
Warning(fs/gfs2/aops.c:236): No description found for parameter 'end'
Warning(fs/gfs2/aops.c:236): No description found for parameter 'done_index'
Warning(fs/gfs2/aops.c:236): Excess function parameter 'writepage' description in 'gfs2_write_jdata_pagevec'
Warning(fs/gfs2/aops.c:346): Excess function parameter 'writepage' description in 'gfs2_write_cache_jdata'
Warning(fs/gfs2/aops.c:346): Excess function parameter 'data' description in 'gfs2_write_cache_jdata'
Warning(fs/gfs2/aops.c:605): No description found for parameter 'file'
Warning(fs/gfs2/aops.c:605): No description found for parameter 'mapping'
Warning(fs/gfs2/aops.c:605): No description found for parameter 'pages'
Warning(fs/gfs2/aops.c:605): No description found for parameter 'nr_pages'
Warning(fs/gfs2/aops.c:870): No description found for parameter 'copied'

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>