mei: don't mix read and write slots

Do not pass read slots pointer into function
mei_irq_thread_write_handler, the write
slots management is handled internally in the write
handler

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>