cyrpto: powerpc/aes - delete the rebundant word "block" in comments

 * instructions per clock cycle using one 32/64 bit unit (SU1) and one 32

 * bit unit (SU2). One of these can be a memory access that is executed via

 * a single load and store unit (LSU). XTS-AES-256 takes ~780 operations per

 * 16 byte block block or 25 cycles per byte. Thus 768 bytes of input data

 * 16 byte block or 25 cycles per byte. Thus 768 bytes of input data

 * will need an estimated maximum of 20,000 cycles. Headroom for cache misses

 * included. Even with the low end model clocked at 667 MHz this equals to a

 * critical time window of less than 30us. The value has been chosen to