Fix compiler warnings seen with clang-powerpc64le target
* cipher/rijndael-ppc-common.h (asm_sbox_be): New.
* cipher/rijndael-ppc.c (_gcry_aes_sbox4_ppc8): Use 'asm_sbox_be'
instead of 'vec_sbox_be' since this instrinsics has different
prototype definition on GCC and Clang ('vector uchar' vs 'vector
ulong long').
* cipher/sha256-ppc.c (vec_ror_u32): Remove unused function.- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>