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

there is rebundant word "block" in comments, so remove it
Signed-off-by: Nshaom Deng <dengshaomin@cdjrlc.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/powerpc/crypto/aes-spe-glue.c

@@ -28,7 +28,7 @@
  * 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