crypto: powerpc/crc-vpmsum_test - Fix sparse endianness warning

This patch fixes a sparse endianness warning by changing crc32 to
__le32 instead of u32:

  CHECK   ../arch/powerpc/crypto/crc-vpmsum_test.c
../arch/powerpc/crypto/crc-vpmsum_test.c:102:39: warning: cast from restricted __le32

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>