crypto: bfin_crc - replace sg_count by sg_nents

The sg_count function in bfin_crc.c is the same function as sg_nents.
Remove the duplicate code and use sg_nents() instead.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>