staging: r8188eu: remove write-only variable cpwm

cpwm in struct pwrctrl_priv is never read. Remove it.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210911141521.24901-4-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>