crypto: caam - fix unchecked return value error

error:
Unchecked return value (CHECKED_RETURN)
check_return: Calling sg_miter_next without checking return value

fix:
added check if(!sg_miter_next)

Fixes: 8a2a0dd3 ("crypto: caam - strip input zeros from RSA input buffer")
Signed-off-by: Gaurav Jain <gaurav.jain@nxp.com>
Signed-off-by: Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
Reviewed-by: Gaurav Jain <gaurav.jain@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>