media: cx231xx: Add EP5_BUF_SIZE and EP5_TIMEOUT_MS macros

Define EP5_BUF_SIZE and EP5_TIMEOUT_MS macros to make the code
more readable.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Suggested-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>