gfs2: Kill gfs2_io_error_bh_wd

gfs2: Kill gfs2_io_error_bh_wd

All callers of gfs2_io_error_bh() call gfs2_withdraw() as well, so
change gfs2_io_error_bh() to call gfs2_withdraw() directly.  This also
brings it in line with other similar error reporting functions.

With that, gfs2_io_error_bh() is the same as gfs2_io_error_bh_wd(), so
remove the latter.

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