RDMA/siw: Use max() instead of doing it manually

Fix following coccicheck warning:

./drivers/infiniband/sw/siw/siw_verbs.c:665:28-29: WARNING opportunity for max().

Link: https://lore.kernel.org/r/1638439679-114250-1-git-send-email-jiapeng.chong@linux.alibaba.comReported-by: NAbaci Robot <abaci@linux.alibaba.com>
Signed-off-by: NJiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: NBernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/siw/siw_verbs.c

@@ -662,7 +662,7 @@ static int siw_copy_inline_sgl(const struct ib_send_wr *core_wr,
 		kbuf += core_sge->length;
 		core_sge++;
 	}
-	sqe->sge[0].length = bytes > 0 ? bytes : 0;
+	sqe->sge[0].length = max(bytes, 0);
 	sqe->num_sge = bytes > 0 ? 1 : 0;
 
 	return bytes;