wifi: mwifiex: mwifiex_process_sleep_confirm_resp(): remove unused priv variable

Clang static analyzer complains that value stored to 'priv' is never read.
'priv' is useless, so remove it to save space.

Signed-off-by: Su Hui <suhui@nfschina.com>
Acked-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231115092328.1048103-1-suhui@nfschina.com