crypto: qat - use struct_size() helper

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct qat_alg_buf_list {
	...
        struct qat_alg_buf bufers[];
} __packed __aligned(64);

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

So, replace the following form:

sizeof(struct qat_alg_buf_list) + ((1 + n) * sizeof(struct qat_alg_buf))

with:

struct_size(bufl, bufers, n + 1)

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>