kunit: Fix checksum tests on big endian CPUs

On powerpc64le checksum kunit tests work:

[    2.011457][    T1]     KTAP version 1
[    2.011662][    T1]     # Subtest: checksum
[    2.011848][    T1]     1..3
[    2.034710][    T1]     ok 1 test_csum_fixed_random_inputs
[    2.079325][    T1]     ok 2 test_csum_all_carry_inputs
[    2.127102][    T1]     ok 3 test_csum_no_carry_inputs
[    2.127202][    T1] # checksum: pass:3 fail:0 skip:0 total:3
[    2.127533][    T1] # Totals: pass:3 fail:0 skip:0 total:3
[    2.127956][    T1] ok 1 checksum

But on powerpc64 and powerpc32 they fail:

[    1.859890][    T1]     KTAP version 1
[    1.860041][    T1]     # Subtest: checksum
[    1.860201][    T1]     1..3
[    1.861927][   T58]     # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_kunit.c:243
[    1.861927][   T58]     Expected result == expec, but
[    1.861927][   T58]         result == 54991 (0xd6cf)
[    1.861927][   T58]         expec == 33316 (0x8224)
[    1.863742][    T1]     not ok 1 test_csum_fixed_random_inputs
[    1.864520][   T60]     # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:267
[    1.864520][   T60]     Expected result == expec, but
[    1.864520][   T60]         result == 255 (0xff)
[    1.864520][   T60]         expec == 65280 (0xff00)
[    1.868820][    T1]     not ok 2 test_csum_all_carry_inputs
[    1.869977][   T62]     # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:306
[    1.869977][   T62]     Expected result == expec, but
[    1.869977][   T62]         result == 64515 (0xfc03)
[    1.869977][   T62]         expec == 0 (0x0)
[    1.872060][    T1]     not ok 3 test_csum_no_carry_inputs
[    1.872102][    T1] # checksum: pass:0 fail:3 skip:0 total:3
[    1.872458][    T1] # Totals: pass:0 fail:3 skip:0 total:3
[    1.872791][    T1] not ok 3 checksum

This is because all expected values were calculated for X86 which
is little endian. On big endian systems all precalculated 16 bits
halves must be byte swapped.

And this is confirmed by a huge amount of sparse errors when building
with C=2

So fix all sparse errors and it will naturally work on all endianness.

Fixes: 688eb819 ("x86/csum: Improve performance of `csum_partial`")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>