GFS2: fs/gfs2/bmap.c: kernel-doc warning fixes

Fix 2 typos and move one definition which was between function
comments and function definition (yet another kernel-doc warning)

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>