hfs/hfsplus: use WARN_ON for sanity check

hfs/hfsplus: use WARN_ON for sanity check

gcc warns about a couple of instances in which a sanity check exists but
the author wasn't sure how to react to it failing, which makes it look
like a possible bug:

  fs/hfsplus/inode.c: In function 'hfsplus_cat_read_inode':
  fs/hfsplus/inode.c:503:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    503 |                         /* panic? */;
        |                                     ^
  fs/hfsplus/inode.c:524:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    524 |                         /* panic? */;
        |                                     ^
  fs/hfsplus/inode.c: In function 'hfsplus_cat_write_inode':
  fs/hfsplus/inode.c:582:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    582 |                         /* panic? */;
        |                                     ^
  fs/hfsplus/inode.c:608:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    608 |                         /* panic? */;
        |                                     ^
  fs/hfs/inode.c: In function 'hfs_write_inode':
  fs/hfs/inode.c:464:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    464 |                         /* panic? */;
        |                                     ^
  fs/hfs/inode.c:485:37: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
    485 |                         /* panic? */;
        |                                     ^

panic() is probably not the correct choice here, but a WARN_ON
seems appropriate and avoids the compile-time warning.

Link: https://lkml.kernel.org/r/20210927102149.1809384-1-arnd@kernel.org
Link: https://lore.kernel.org/all/20210322223249.2632268-1-arnd@kernel.org/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>