crypto: hisilicon/sgl - small cleanups for sgl.c

1. Remove unnecessary brackets in function hisi_acc_create_sgl_pool().
2. Modify local variable type, ensure that the variable type is
consistent with the variable type to be compared.
3. Because the function clear_hw_sgl_sge() is in the task process,
obtain the value of le16_to_cpu(hw_sgl->entry_sum_in_sgl) before
loop execting to shorten the loop execution time.

Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>