gfs2: print mapping->nrpages in glock dump for address space glocks

This patch makes the glock dumps in debugfs print the number of pages
(nrpages) for address space glocks. This will aid in debugging.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>