x86/csum: Fix clang -Wuninitialized in csum_partial()

Clang warns:

  arch/x86/lib/csum-partial_64.c:74:20: error: variable 'result' is uninitialized when used here [-Werror,-Wuninitialized]
                  return csum_tail(result, temp64, odd);
                                   ^~~~~~
  arch/x86/lib/csum-partial_64.c:48:22: note: initialize the variable 'result' to silence this warning
          unsigned odd, result;
                              ^
                               = 0
  1 error generated.

The only initialization and uses of result in csum_partial() were moved
into csum_tail() but result is still being passed by value to
csum_tail() (clang's -Wuninitialized does not do interprocedural
analysis to realize that result is always assigned in csum_tail()
however). Sink the declaration of result into csum_tail() to clear up
the warning.

Closes: https://lore.kernel.org/202305262039.3HUYjWJk-lkp@intel.com/


Fixes: 688eb819 ("x86/csum: Improve performance of `csum_partial`")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20230526-csum_partial-wuninitialized-v1-1-ebc0108dcec1%40kernel.org