jfs: don't bother with make_bad_inode() in ialloc()

We hit that when inumber allocation has failed.  In that case
the in-core inode is not hashed and since its ->i_nlink is 1
the only place where jfs checks is_bad_inode() won't be reached.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>