crypto: talitos - fix bug in sg_copy_end_to_buffer

In function sg_copy_end_to_buffer, too much data
is copied when a segment in the scatterlist
has .length greater than the requested copy length.

This patch adds the limit checks to fix this bug of over copying,
which affected only the ahash algorithms.

Signed-off-by: Lee Nipper <lee.nipper@gmail.com>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>