current_desc_hdr() returns a u32 but in fact this is a __be32,
leading to a lot of sparse warnings.

Change the return type to __be32 and ensure it is handled as
sure by the caller.

Fixes: 3e721aeb ("crypto: talitos - handle descriptor not found in error path")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>