crypto: sa2ul - change unsafe data size limit to 255 bytes

256 bytes is quite often used in performance benchmarks and this size
appears to be also working just fine, so mark it as safe so that we do
not fallback to software implementation for this packet size. Otherwise
there is a strange bump up in crypto performance at 256 byte packet size.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>