Remove set but not used variable in ddt.c

[mcmilk]

Description

While testing the qemu runners, FreeBSD does not build the module right now.

This is the error we have:

  --- ddt.o ---
886
  /usr/home/zfs/zfs/module/zfs/ddt.c:2612:6: error: variable 'total' set but not used [-Werror,-Wunused-but-set-variable]
887
   2612 |         int total = 0, valid = 0;
888
        |             ^
889
  1 error generated.
890
  *** [ddt.o] Error code 1

@don-brady: I removed this (testing?) variable.

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[amotin]

I am not sure whether total or valid use would look more correct in the debug message, the only place they are used, but counting both indeed seems redundant.