staging: rtlwifi: Remove unused variable

This removes an unused variable to silence the associated build warning.

Fixes: f8af6a32 ("staging: rtlwifi: Convert timers to use timer_setup()")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>