gfs2: Remove unnecessary gfs2_meta_check_ii argument

The type argument of gfs2_meta_check_ii() is always set to "magic
number", so remove that argument and hardcode the string in
gfs2_meta_check_ii().  Change the string to "bad magic number" to
emphasize that the problem is the incorrect magic number.

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